Patent Application
20220298517
This application contains a Sequence Listing in computer-readable form, which is incorporated herein by reference.
The present invention relates to method for counter-selection by inhibition of conditionally essential genes.
The so-called CRISPR genome editing system has been widely used as a tool to modify the genomes of a number of organisms. The power of the CRISPR system lies in its simplicity and its ability to target and edit down to a single base pair in a specific gene of interest. The system relies on CRISPR-associated proteins (Cas), which are RNA-guided endonucleases, as well as so-called guide-RNA (gRNA) molecules that are able to form a complex with the endonuclease and direct the nuclease activity to a particular DNA sequence. The choice of DNA target sequence is made by varying the nucleotide sequence of the gRNA to match the target DNA sequence. When complexed with the gRNA molecule, the endonuclease can recognize and bind its target DNA sequence, forming an endonuclease-gRNA-DNA complex, and create a double-stranded break using its catalytic domain(s).
For genome editing purposes, the most widely used CRISPR-associated proteins are those of Class 2, which include Cas9 (Cas type II) derived from Streptococcus pyogenes and Cpf1 (Cas type V) derived from Acidaminococcus or Lachnospiraceae. Another example of an RNA-guided endonuclease is Mad7 isolated from Eubacterium rectale. Although there are some structural similarities between Mad7 and Cpf1, Mad7 is only 31% conserved with Cpf1 from Acidominococcus sp. at the amino acid level.
In addition to its use within genome editing, the CRISPR system can also be used to control gene expression. This application, often referred to as CRISPR interference or CRISPRi, allows sequence-specific repression or activation of a gene. CRISPR interference utilizes a catalytically inactive (“dead”) endonuclease variant (e.g., Mad7d) that can be obtained by introducing amino acid mutations in the catalytic domain responsible for endonuclease activity. Upon association with gRNA, the resulting complex retains the ability to bind to the target DNA sequence but cannot introduce any breaks in the DNA strand. As long as the catalytically inactive endonuclease is bound to the target DNA sequence, expression of the target sequence is repressed. By varying the gRNA sequence, one can control the target DNA sequence and thereby regulate the expression of virtually any gene in any organism.
Within industrial biotechnology, there is a continued need for robust and effective selection systems suitable for development of optimized production hosts. Given the versatility and precision of the CRISPR technology, it has been speculated that this system could be harnessed for counter-selection purposes. However, attempts of utilizing the CRISPR technology for direct selection have so far been difficult. This is especially true for bacterial host cells, since many prokaryotic organisms are very sensitive to the endonuclease activity of the RNA-guided endonuclease-gRNA complex due to the inefficient repair mechanisms for double-stranded (DS) breaks by non-homologous end-joining (NHEJ) systems that are known from eukaryotes (see, e.g., Su et al., Scientific Reports 2016, 6, 37895; Altenbuchner, Applied and Environmental Microbiology 2016, 82, pp. 5421-5427; Peters et al., Current Opinion in Microbiology 2015, 27, pp. 121-126; Aravind and Koonin, Genome Research 2001, 11, pp. 1365-1374). Moreover, in many cases it is desirable to introduce several copies of a gene or operon (expression cassette) to maximize the yield of a given polypeptide of interest. However, the direct selection using the CRISPR technology will be increasingly difficult if more than one site is targeted for DS breaks in an effort to introduce multiple expression cassettes in one process.
Researchers have reported successful integration of a gene of interest (GOI) by homologous recombination (HR) into a gRNA target on chromosome and then introduce endonuclease activity for DS breaks to kill the cells which has retained the original gRNA target sequence. In this way, it is possible to efficiently enrich for cells which have received the GOI. However, the timing of these events of HR and DS activity are very important. RNA-guided endonucleases are typically very active in generating DS breaks and should not be expressed until homologous recombination has occurred and removed the target.
The present invention provides means and methods for utilizing the versatility and precision of the CRISPR technology in a selection system suitable for microbial host cells.
Thus, in a first aspect, the present invention relates to a method for inserting at least one polynucleotide of interest into the genome of a host cell, the method comprising the steps of:
In a second aspect, the present invention relates to a method for inserting at least two different polynucleotides of interest into the genome of a host cell, the method comprising the steps of:
cDNA: The term “cDNA” means a DNA molecule that can be prepared by reverse transcription from a mature, spliced, mRNA molecule obtained from a eukaryotic or prokaryotic cell. cDNA lacks intron sequences that may be present in the corresponding genomic DNA. The initial, primary RNA transcript is a precursor to mRNA that is processed through a series of steps, including splicing, before appearing as mature spliced mRNA.
Coding sequence: The term “coding sequence” means a polynucleotide, which directly specifies the amino acid sequence of a polypeptide. The boundaries of the coding sequence are generally determined by an open reading frame, which begins with a start codon such as ATG, GTG, or TTG and ends with a stop codon such as TAA, TAG, or TGA. The coding sequence may be a genomic DNA, cDNA, synthetic DNA, or a combination thereof.
Conditionally essential gene: A conditionally essential gene or locus may function as a selectable marker. Examples of bacterial conditionally essential selectable markers are the dal genes from Bacillus subtilis or Bacillus licheniformis, that are only essential when the bacterium is cultivated in the presence of D-alanine; or the genes encoding enzymes involved in the removal of UDP-galactose from the bacterial cell when the cell is grown in the presence of galactose. Non-limiting examples of such genes are those from B. subtilis or B. licheniformis encoding UTP-dependent phosphorylase (EC 2.7.7.10), UDP-glucose-dependent uridylyltransferase (EC 2.7.7.12), or UDP-galactose epimerase (EC 5.1.3.2). If an essential gene or locus is inactivated, it will render the resulting strain with a deficiency, e.g. being unable to metabolize a specific carbon-source, or a growth requirement, e.g., becoming amino acid auxotrophic, or becoming sensitive to a given stress. Non-limiting examples of conditionally essential genes are D-alanine racemase-encoding genes, xylose isomerase-encoding genes, and genes of the gluconate operon. Preferably the conditionally essential gene are chosen from the group consisting of dal, lysA, araA, galE, antK, metC, xylA, gntP, gntK, glpD, glpF, glpK, glpP, lacA2, hisC, gapA, and aspB.
Control sequences: The term “control sequences” means nucleic acid sequences necessary for expression of a polynucleotide encoding a mature polypeptide of the present invention. Each control sequence may be native (i.e., from the same gene) or foreign (i.e., from a different gene) to the polynucleotide encoding the polypeptide or native or foreign to each other. Such control sequences include, but are not limited to, a leader, polyadenylation sequence, propeptide sequence, promoter, signal peptide sequence, and transcription terminator. At a minimum, the control sequences include a promoter, and transcriptional and translational stop signals. The control sequences may be provided with linkers for the purpose of introducing specific restriction sites facilitating ligation of the control sequences with the coding region of the polynucleotide encoding a polypeptide.
Expression: The term “expression” includes any step involved in the production of a polypeptide including, but not limited to, transcription, post-transcriptional modification, translation, post-translational modification, and secretion.
Expression vector: The term “expression vector” means a linear or circular DNA molecule that comprises a polynucleotide encoding a polypeptide and is operably linked to control sequences that provide for its expression.
Host cell: The term “host cell” means any cell type that is susceptible to transformation, transfection, transduction, or the like with a nucleic acid construct or expression vector comprising a polynucleotide of the present invention. The term “host cell” encompasses any progeny of a parent cell that is not identical to the parent cell due to mutations that occur during replication.
Isolated: The term “isolated” means a substance in a form or environment that does not occur in nature. Non-limiting examples of isolated substances include (1) any non-naturally occurring substance, (2) any substance including, but not limited to, any enzyme, variant, nucleic acid, protein, peptide or cofactor, that is at least partially removed from one or more or all of the naturally occurring constituents with which it is associated in nature; (3) any substance modified by the hand of man relative to that substance found in nature; or (4) any substance modified by increasing the amount of the substance relative to other components with which it is naturally associated (e.g., recombinant production in a host cell; multiple copies of a gene encoding the substance; and use of a stronger promoter than the promoter naturally associated with the gene encoding the substance). An isolated substance may be present in a fermentation broth sample; e.g. a host cell may be genetically modified to express the polypeptide of the invention. The fermentation broth from that host cell will comprise the isolated polypeptide.
Nuclease-null: The term “nuclease-null” is used to described RNA-guided endonucleases for which endonuclease activity has been disrupted. A nuclease-null variant of an RNA-guided endonuclease can bind to its target DNA sequence but cannot introduce any breakes in the target DNA sequence. The terms “nuclease-null”, “catalytically inactive”, and “dead” (abbreviated “d”, e.g., Mad7d) are used interchangeably herein.
Nucleic acid construct: The term “nucleic acid construct” means a nucleic acid molecule, either single- or double-stranded, which is isolated from a naturally occurring gene or is modified to contain segments of nucleic acids in a manner that would not otherwise exist in nature or which is synthetic, which comprises one or more control sequences.
Operably linked: The term “operably linked” means a configuration in which a control sequence is placed at an appropriate position relative to the coding sequence of a polynucleotide such that the control sequence directs expression of the coding sequence.
RNA-guided endonuclease: The term “RNA-guided endonuclease” means a polypeptide having endonuclease activity, wherein the endonuclease activity is controlled by one or more gRNA that form a complex with the RNA-guided endonuclease and directs the endonuclease activity to a target DNA sequence that is complementary to and capable of hybridizing to the one or more gRNA.
Sequence identity: The relatedness between two amino acid sequences or between two nucleotide sequences is described by the parameter “sequence identity”.
For purposes of the present invention, the sequence identity between two amino acid sequences is determined using the Needleman-Wunsch algorithm (Needleman and Wunsch, 1970, J. Mol. Biol. 48: 443-453) as implemented in the Needle program of the EMBOSS package (EMBOSS: The European Molecular Biology Open Software Suite, Rice et al., 2000, Trends Genet. 16: 276-277), preferably version 5.0.0 or later. The parameters used are gap open penalty of 10, gap extension penalty of 0.5, and the EBLOSUM62 (EMBOSS version of BLOSUM62) substitution matrix. The output of Needle labeled “longest identity” (obtained using the-nobrief option) is used as the percent identity and is calculated as follows:
(Identical Residues×100)/(Length of Alignment−Total Number of Gaps in Alignment)
For purposes of the present invention, the sequence identity between two deoxyribonucleotide sequences is determined using the Needleman-Wunsch algorithm (Needleman and Wunsch, 1970, supra) as implemented in the Needle program of the EMBOSS package (EMBOSS: The European Molecular Biology Open Software Suite, Rice et al., 2000, supra), preferably version 5.0.0 or later. The parameters used are gap open penalty of 10, gap extension penalty of 0.5, and the EDNAFULL (EMBOSS version of NCBI NUC4.4) substitution matrix. The output of Needle labeled “longest identity” (obtained using the -nobrief option) is used as the percent identity and is calculated as follows:
(Identical Deoxyribonucleotides×100)/(Length of Alignment−Total Number of Gaps in Alignment)
Sequence complementarity: The relatedness between two complementary nucleotide sequences is described by the parameter “sequence complementarity” and is determined using the same algorithm as for sequence identity, wherein the anti-sense complementary sequence is converted to its sense sequence before alignment and calculation.
The present invention provides means and methods for utilizing the versatility and precision of the CRISPR technology in a selection system suitable for microbial host cells. By using the DNA sequence encoding the gRNA (denoted ‘gDNA’) in CRISPRi as an indirect counter-selectable marker, the present inventors have shown that multiple gene copies can be inserted into the genome of a host cell by selection for the absence of the gDNA encoding the gRNA.
As illustrated in the Examples herein, a suitable selection system may be based on an antibiotics resistance gene such as the cat gene that confers resistance to chloramphenicol. A host cell comprising a polynucleotide encoding the cat gene as well as a polynucleotide encoding a nuclease-null variant of an RNA-guided endonuclease and a polynucleotide encoding a gRNA directed towards the cat gene will thus only grow only in the absence of chloramphenicol, since the endonuclease-gRNA complex will repress expression of the cat gene. As long as the nuclease-null variant of RNA-guided endonuclease and the gRNA is expressed by the host cell, the host cell remain sensitive to chloramphenicol.
In a next step, the host cell is transformed with a polynucleotide that allows for replacement of the gDNA with a gene of interest. By subsequent selection for chloramphenicol resistance, only the cells having the gDNA replaced with the gene of interest will survive, since the gRNA is no longer expressed, which makes the properly transformed host cells resistant to chloramphenicol.
As illustrated in the Examples enclosed herein, the methods of the present invention are particularly suitable for one-step multi-insertions of one or more specific expression cassettes on separate loci on the chromosome of a host cell. The method of the invention provides host cells containing multiple expression cassettes, i.e., multi-copy host cells, that are highly stabile due to the expression cassettes being inserted on separate loci on the chromosome. Such cells are highly warranted in industrial biotechnology as robust workhorses for production of polypeptides of interest.
Thus, in a first aspect, the present invention relates to a method for inserting at least one polynucleotide of interest into the genome of a host cell, the method comprising the steps of:
The host cell provided in step (a) of the method of the first aspect comprises at least one polynucleotide encoding a gRNA. Preferably, the number of polynucleotides encoding a gRNA is at least one, such as at least two, at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least 15, at least 20, at least 25, or more.
The host cell is transformed in step (b) of the method of the first aspect with at least one polynucleotide of interest. Preferably, the number of polynucleotide of interest is at least one, such as at least two, at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least 15, at least 20, at least 25, or more.
In a preferred embodiment of the first aspect, the at least one polynucleotide of interest encodes a polypeptide; preferably the polypeptide comprise an enzyme; more preferably the enzyme is selected from the group consisting of hydrolase, isomerase, ligase, lyase, oxidoreductase, or transferase; most preferably the enzyme is selected from the group consisting of an aminopeptidase, amylase, carbohydrase, carboxypeptidase, catalase, cellobiohydrolase, cellulase, chitinase, cutinase, cyclodextrin glycosyltransferase, deoxyribonuclease, endoglucanase, esterase, alpha-galactosidase, beta-galactosidase, glucoamylase, alpha-glucosidase, beta-glucosidase, invertase, laccase, lipase, mannosidase, mutanase, oxidase, pectinolytic enzyme, peroxidase, phosphodiesterase, phytase, polyphenoloxidase, proteolytic enzyme, ribonuclease, transglutaminase, xylanase, and beta-xylosidase.
Preferably, the selectable marker is a positive selection marker, a negative selection marker, a bidirectional marker, or a conditionally essential gene.
Preferably, the selectable marker is an antibiotic resistance gene conferring resistance to chloramphenicol, tetracycline, ampicillin, spectinoymycin, kanamycin, or neomycin; more preferably, the selectable marker is an antibiotic resistance gene conferring resistance to chloramphenicol.
Also preferably, the selectable marker is an antibiotic resistance gene selected from the group consisting of cat, erm, tet, amp, spec, kana, and neo; more preferably, the selectable marker is a cat gene.
Alternatively, and also preferably, the selectable marker is a gene conferring auxotrophy to the host cell. Preferably, the selectable marker is a conditionally essential gene selected from the group consisting of dal, lysA, araA, galE, antK metC, xylA, gntP, glpD, glpF, glpK, glpP, lacA2, hisC, gapA, and aspB gene. More preferably, the selectable marker is a dal gene.
There are many well-known ways to inactivate a gene, for example by mutating the gene through the introduction of a non-sense mutation or a frameshift mutation, or by partial or full deletion of the open reading frame, or by manipulation of one or more control sequence.
Accordingly, in a preferred embodiment of the first aspect, the at least one polynucleotide encoding a gRNA is inactivated by partial or full deletion of said polynucleotide.
In a preferred embodiment of the first aspect, the at least one polynucleotide encoding the gRNA has been partially or fully replaced in the genome of the host cell by the at least one polynucleotide of interest in step (d), thereby inactivating the at least one polynucleotide encoding the gRNA.
In a second aspect, the present invention relates to a method for inserting at least two different polynucleotides of interest into the genome of a host cell, the method comprising the steps of:
The host cell provided in step (a) of the method of the second aspect comprises at least two polynucleotides encoding at least two different selectable markers and at least two polynucleotides encoding at least two gRNAs. Preferably, the number of polynucleotides encoding the at least two different selectable markers and the at least two gRNAs are, independently, at least two, such as at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least 15, at least 20, at least 25, or more.
The host cell is transformed in step (b) of the method of the second aspect with at least two different polynucleotides of interest. Preferably, the number of different polynucleotides of interest is at least two, such as at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least 15, at least 20, at least 25, or more.
In a preferred embodiment of the second aspect, the at least two different polynucleotides of interest encode at least two polypeptides; preferably the at least two polypeptides comprise at least two enzymes; more preferably the at least two enzymes are independently selected from the group consisting of hydrolase, isomerase, ligase, lyase, oxidoreductase, or transferase; most preferably the at least two enzymes are independently selected from the group consisting of aminopeptidase, amylase, carbohydrase, carboxypeptidase, catalase, cellobiohydrolase, cellulase, chitinase, cutinase, cyclodextrin glycosyltransferase, deoxyribonuclease, endoglucanase, esterase, alpha-galactosidase, beta-galactosidase, glucoamylase, alpha-glucosidase, beta-glucosidase, invertase, laccase, lipase, mannosidase, mutanase, oxidase, pectinolytic enzyme, peroxidase, phosphodiesterase, phytase, polyphenoloxidase, proteolytic enzyme, ribonuclease, transglutaminase, xylanase, and beta-xylosidase.
Preferably, the at least two different selectable markers are, independently, positive selection markers, negative selection marker, bidirectional markers, or conditionally essential genes.
Preferably, the at least two different selectable markers are antibiotic resistance genes selected from the group consisting of cat, erm, tet, amp, spec, kana, and neo.
Preferably, the at least two different selectable markers are genes conferring auxotrophy to the host cell. Preferably, the selectable markers are conditionally essential genes selected from the group consisting of dal, lysA, araA, galE, antK metC, xylA, gntP, glpD, glpF, glpK, glpP, lacA2, hisC, gapA, and aspB gene.
Preferably, the at least two different selectable markers are, independently, selected from the group consisting of antibiotic resistance genes and genes conferring auxotrophy to the host cell; preferably, the at least two different selectable markers are, independently, selected from the group of genes consisting of cat, erm, tet, amp, spec, kana, neo, dal, lysA, araA, galE, antK metC, xylA, gntP, glpD, glpF, glpK, glpP, lacA2, hisC, gapA, and aspB.
Preferably, the at least two polynucleotides encoding the at least two gRNAs are inactivated by partial or full deletion of said polynucleotides.
Preferably, the at least two polynucleotides encoding the at least two gRNAs have been partially or fully replaced in the genome of the host cell by the at least two different polynucleotides of interest in step (d), thereby inactivating the at least two polynucleotides encoding the at least two gRNAs.
The present invention also relates to polynucleotides of the invention, including polynucleotides of interest as a well as polynucleotides encoding selectable markers, gRNAs, and nuclease-null variants of an RNA-guided endonuclease. In an embodiment, such polynucleotides have been isolated.
The techniques used to isolate or clone a polynucleotide are known in the art and include isolation from genomic DNA or cDNA, or a combination thereof. The cloning of the polynucleotides from genomic DNA can be affected, e.g., by using the well-known polymerase chain reaction (PCR) or antibody screening of expression libraries to detect cloned DNA fragments with shared structural features. See, e.g., Innis et al., 1990, PCR: A Guide to Methods and Application, Academic Press, New York. Other nucleic acid amplification procedures such as ligase chain reaction (LCR), ligation activated transcription (LAT) and polynucleotide-based amplification (NASBA) may be used.
The present invention also relates to nucleic acid constructs comprising a polynucleotide of the present invention operably linked to one or more control sequences that direct the expression of the coding sequence in a suitable host cell under conditions compatible with the control sequences.
The polynucleotides may be manipulated in a variety of ways to provide for their expression. Manipulation of the polynucleotide prior to its insertion into a vector may be desirable or necessary depending on the expression vector. The techniques for modifying polynucleotides utilizing recombinant DNA methods are well known in the art.
The control sequence may be a promoter, a polynucleotide that is recognized by a host cell for expression of a polynucleotide encoding a polypeptide of the present invention. The promoter contains transcriptional control sequences that mediate the expression of the polypeptide. The promoter may be any polynucleotide that shows transcriptional activity in the host cell including variant, truncated, and hybrid promoters, and may be obtained from genes encoding extracellular or intracellular polypeptides either homologous or heterologous to the host cell.
Examples of suitable promoters for directing transcription of the nucleic acid constructs of the present invention in a bacterial host cell are the promoters obtained from the Bacillus amyloliquefaciens alpha-amylase gene (amyQ), Bacillus licheniformis alpha-amylase gene (amyL), Bacillus licheniformis penicillinase gene (penP), Bacillus stearothermophilus maltogenic amylase gene (amyM), Bacillus subtilis levansucrase gene (sacB), Bacillus subtilis xylA and xylB genes, Bacillus thuringiensis ctylIIA gene (Agaisse and Lereclus, 1994, Molecular Microbiology 13: 97-107), E. coli lac operon, E. coli trc promoter (Egon et al., 1988, Gene 69: 301-315), Streptomyces coelicolor agarase gene (dagA), and prokaryotic beta-lactamase gene (Villa-Kamaroff et al., 1978, Proc. Natl. Acad. Sci. USA 75: 3727-3731), as well as the tac promoter (DeBoer et al., 1983, Proc. Natl. Acad. Sci. USA 80: 21-25). Further promoters are described in “Useful proteins from recombinant bacteria” in Gilbert et al., 1980, Scientific American 242: 74-94; and in Sambrook et al., 1989, supra. Examples of tandem promoters are disclosed in WO 99/43835.
Examples of suitable promoters for directing transcription of the nucleic acid constructs of the present invention in a filamentous fungal host cell are promoters obtained from the genes for Aspergillus nidulans acetamidase, Aspergillus niger neutral alpha-amylase, Aspergillus niger acid stable alpha-amylase, Aspergillus niger or Aspergillus awamori glucoamylase (glaA), Aspergillus oryzae TAKA amylase, Aspergillus oryzae alkaline protease, Aspergillus oryzae triose phosphate isomerase, Fusarium oxysporum trypsin-like protease (WO 96/00787), Fusarium venenatum amyloglucosidase (WO 00/56900), Fusarium venenatum Dania (WO 00/56900), Fusarium venenatum Quinn (WO 00/56900), Rhizomucor miehei lipase, Rhizomucor miehei aspartic proteinase, Trichoderma reesei beta-glucosidase, Trichoderma reesei cellobiohydrolase I, Trichoderma reesei cellobiohydrolase II, Trichoderma reesei endoglucanase I, Trichoderma reesei endoglucanase II, Trichoderma reesei endoglucanase III, Trichoderma reesei endoglucanase V, Trichoderma reesei xylanase I, Trichoderma reesei xylanase II, Trichoderma reesei xylanase III, Trichoderma reesei beta-xylosidase, and Trichoderma reesei translation elongation factor, as well as the NA2-tpi promoter (a modified promoter from an Aspergillus neutral alpha-amylase gene in which the untranslated leader has been replaced by an untranslated leader from an Aspergillus triose phosphate isomerase gene; non-limiting examples include modified promoters from an Aspergillus niger neutral alpha-amylase gene in which the untranslated leader has been replaced by an untranslated leader from an Aspergillus nidulans or Aspergillus oryzae triose phosphate isomerase gene); and variant, truncated, and hybrid promoters thereof. Other promoters are described in U.S. Pat. No. 6,011,147.
In a yeast host, useful promoters are obtained from the genes for Saccharomyces cerevisiae enolase (ENO-1), Saccharomyces cerevisiae galactokinase (GAL1), Saccharomyces cerevisiae alcohol dehydrogenase/glyceraldehyde-3-phosphate dehydrogenase (ADH1, ADH2/GAP), Saccharomyces cerevisiae triose phosphate isomerase (TPI), Saccharomyces cerevisiae metallothionein (CUP1), and Saccharomyces cerevisiae 3-phosphoglycerate kinase. Other useful promoters for yeast host cells are described by Romanos et al., 1992, Yeast 8: 423-488.
The control sequence may also be a transcription terminator, which is recognized by a host cell to terminate transcription. The terminator is operably linked to the 3′-terminus of the polynucleotide. Any terminator that is functional in the host cell may be used in the present invention.
Preferred terminators for bacterial host cells are obtained from the genes for Bacillus clausii alkaline protease (aprH), Bacillus licheniformis alpha-amylase (amyL), and Escherichia coli ribosomal RNA (rrnB).
Preferred terminators for filamentous fungal host cells are obtained from the genes for Aspergillus nidulans acetamidase, Aspergillus nidulans anthranilate synthase, Aspergillus niger glucoamylase, Aspergillus niger alpha-glucosidase, Aspergillus oryzae TAKA amylase, Fusarium oxysporum trypsin-like protease, Trichoderma reesei beta-glucosidase, Trichoderma reesei cellobiohydrolase I, Trichoderma reesei cellobiohydrolase II, Trichoderma reesei endoglucanase I, Trichoderma reesei endoglucanase II, Trichoderma reesei endoglucanase III, Trichoderma reesei endoglucanase V, Trichoderma reesei xylanase I, Trichoderma reesei xylanase II, Trichoderma reesei xylanase III, Trichoderma reesei beta-xylosidase, and Trichoderma reesei translation elongation factor.
Preferred terminators for yeast host cells are obtained from the genes for Saccharomyces cerevisiae enolase, Saccharomyces cerevisiae cytochrome C (CYC1), and Saccharomyces cerevisiae glyceraldehyde-3-phosphate dehydrogenase. Other useful terminators for yeast host cells are described by Romanos et al., 1992, supra.
The control sequence may also be an mRNA stabilizer region downstream of a promoter and upstream of the coding sequence of a gene which increases expression of the gene.
Examples of suitable mRNA stabilizer regions are obtained from a Bacillus thuringiensis crylIIA gene (WO 94/25612) and a Bacillus subtilis SP82 gene (Hue et al., 1995, Journal of Bacteriology 177: 3465-3471).
The control sequence may also be a leader, a nontranslated region of an mRNA that is important for translation by the host cell. The leader is operably linked to the 5′-terminus of the polynucleotide. Any leader that is functional in the host cell may be used.
Preferred leaders for filamentous fungal host cells are obtained from the genes for Aspergillus oryzae TAKA amylase and Aspergillus nidulans triose phosphate isomerase.
Suitable leaders for yeast host cells are obtained from the genes for Saccharomyces cerevisiae enolase (ENO-1), Saccharomyces cerevisiae 3-phosphoglycerate kinase, Saccharomyces cerevisiae alpha-factor, and Saccharomyces cerevisiae alcohol dehydrogenase/glyceraldehyde-3-phosphate dehydrogenase (ADH2/GAP).
The control sequence may also be a polyadenylation sequence, a sequence operably linked to the 3′-terminus of the polynucleotide and, when transcribed, is recognized by the host cell as a signal to add polyadenosine residues to transcribed mRNA. Any polyadenylation sequence that is functional in the host cell may be used.
Preferred polyadenylation sequences for filamentous fungal host cells are obtained from the genes for Aspergillus nidulans anthranilate synthase, Aspergillus niger glucoamylase, Aspergillus niger alpha-glucosidase Aspergillus oryzae TAKA amylase, and Fusarium oxysporum trypsin-like protease.
Useful polyadenylation sequences for yeast host cells are described by Guo and Sherman, 1995, Mol. Cellular Biol. 15: 5983-5990.
The control sequence may also be a signal peptide coding region that encodes a signal peptide linked to the N-terminus of a polypeptide and directs the polypeptide into the cell's secretory pathway. The 5′-end of the coding sequence of the polynucleotide may inherently contain a signal peptide coding sequence naturally linked in translation reading frame with the segment of the coding sequence that encodes the polypeptide. Alternatively, the 5′-end of the coding sequence may contain a signal peptide coding sequence that is foreign to the coding sequence. A foreign signal peptide coding sequence may be required where the coding sequence does not naturally contain a signal peptide coding sequence. Alternatively, a foreign signal peptide coding sequence may simply replace the natural signal peptide coding sequence in order to enhance secretion of the polypeptide. However, any signal peptide coding sequence that directs the expressed polypeptide into the secretory pathway of a host cell may be used.
Effective signal peptide coding sequences for bacterial host cells are the signal peptide coding sequences obtained from the genes for Bacillus NCIB 11837 maltogenic amylase, Bacillus licheniformis subtilisin, Bacillus licheniformis beta-lactamase, Bacillus stearothermophilus alpha-amylase, Bacillus stearothermophilus neutral proteases (nprT, nprS, nprM), and Bacillus subtilis prsA. Further signal peptides are described by Simonen and Palva, 1993, Microbiological Reviews 57: 109-137.
Effective signal peptide coding sequences for filamentous fungal host cells are the signal peptide coding sequences obtained from the genes for Aspergillus niger neutral amylase, Aspergillus niger glucoamylase, Aspergillus oryzae TAKA amylase, Humicola insolens cellulase, Humicola insolens endoglucanase V, Humicola lanuginosa lipase, and Rhizomucor miehei aspartic proteinase.
Useful signal peptides for yeast host cells are obtained from the genes for Saccharomyces cerevisiae alpha-factor and Saccharomyces cerevisiae invertase. Other useful signal peptide coding sequences are described by Romanos et al., 1992, supra.
The control sequence may also be a propeptide coding sequence that encodes a propeptide positioned at the N-terminus of a polypeptide. The resultant polypeptide is known as a proenzyme or propolypeptide (or a zymogen in some cases). A propolypeptide is generally inactive and can be converted to an active polypeptide by catalytic or autocatalytic cleavage of the propeptide from the propolypeptide. The propeptide coding sequence may be obtained from the genes for Bacillus subtilis alkaline protease (aprE), Bacillus subtilis neutral protease (nprT), Myceliophthora thermophila laccase (WO 95/33836), Rhizomucor miehei aspartic proteinase, and Saccharomyces cerevisiae alpha-factor.
Where both signal peptide and propeptide sequences are present, the propeptide sequence is positioned next to the N-terminus of a polypeptide and the signal peptide sequence is positioned next to the N-terminus of the propeptide sequence.
It may also be desirable to add regulatory sequences that regulate expression of the polynucleotides relative to the growth of the host cell. Examples of regulatory sequences are those that cause expression of the polynucleotide to be turned on or off in response to a chemical or physical stimulus, including the presence of a regulatory compound. Regulatory sequences in prokaryotic systems include the lac, tac, and trp operator systems. In yeast, the ADH2 system or GAL1 system may be used. In filamentous fungi, the Aspergillus niger glucoamylase promoter, Aspergillus oryzae TAKA alpha-amylase promoter, and Aspergillus oryzae glucoamylase promoter, Trichoderma reesei cellobiohydrolase I promoter, and Trichoderma reesei cellobiohydrolase II promoter may be used. Other examples of regulatory sequences are those that allow for gene amplification. In eukaryotic systems, these regulatory sequences include the dihydrofolate reductase gene that is amplified in the presence of methotrexate, and the metallothionein genes that are amplified with heavy metals. In these cases, the polynucleotide would be operably linked to the regulatory sequence.
The present invention also relates to recombinant expression vectors comprising a polynucleotide of the present invention, a promoter, and transcriptional and translational stop signals. The various nucleotide and control sequences may be joined together to produce a recombinant expression vector that may include one or more convenient restriction sites to allow for insertion or substitution of the polynucleotide at such sites. Alternatively, the polynucleotide may be expressed by inserting the polynucleotide or a nucleic acid construct comprising the polynucleotide into an appropriate vector for expression. In creating the expression vector, the coding sequence is located in the vector so that the coding sequence is operably linked with the appropriate control sequences for expression.
The recombinant expression vector may be any vector (e.g., a plasmid or virus) that can be conveniently subjected to recombinant DNA procedures and can bring about expression of the polynucleotide. The choice of the vector will typically depend on the compatibility of the vector with the host cell into which the vector is to be introduced. The vector may be a linear or closed circular plasmid.
The vector may be an autonomously replicating vector, i.e., a vector that exists as an extrachromosomal entity, the replication of which is independent of chromosomal replication, e.g., a plasmid, an extrachromosomal element, a minichromosome, or an artificial chromosome. The vector may contain any means for assuring self-replication. Alternatively, the vector may be one that, when introduced into the host cell, is integrated into the genome and replicated together with the chromosome(s) into which it has been integrated. Furthermore, a single vector or plasmid or two or more vectors or plasmids that together contain the total DNA to be introduced into the genome of the host cell, or a transposon, may be used.
The vector preferably contains one or more selectable markers that permit easy selection of transformed, transfected, transduced, or the like cells. A selectable marker is a gene the product of which provides for biocide or viral resistance, resistance to heavy metals, prototrophy to auxotrophs, and the like.
Examples of bacterial selectable markers are Bacillus licheniformis or Bacillus subtilis dal genes, markers that confer auxotrophy for amino acids or other metabolites, or markers that confer antibiotic resistance such as ampicillin, chloramphenicol, kanamycin, neomycin, spectinomycin, or tetracycline resistance. Suitable markers for yeast host cells include, but are not limited to, ADE2, HIS3, LEU2, LYS2, MET3, TRP1, and URA3. Selectable markers for use in a filamentous fungal host cell include, but are not limited to, adeA (phosphoribosylaminoimidazole-succinocarboxamide synthase), adeB (phosphoribosyl-aminoimidazole synthase), amdS (acetamidase), argB (ornithine carbamoyltransferase), bar (phosphinothricin acetyltransferase), hph (hygromycin phosphotransferase), niaD (nitrate reductase), pyrG (orotidine-5′-phosphate decarboxylase), sC (sulfate adenyltransferase), and trpC (anthranilate synthase), as well as equivalents thereof. Preferred for use in an Aspergillus cell are Aspergillus nidulans or Aspergillus oryzae amdS and pyrG genes and a Streptomyces hygroscopicus bar gene. Preferred for use in a Trichoderma cell are adeA, adeB, amdS, hph, and pyrG genes.
The selectable marker may be a dual selectable marker system as described in WO 2010/039889. In one aspect, the dual selectable marker is an hph-tk dual selectable marker system.
The vector preferably contains an element(s) that permits integration of the vector into the host cell's genome or autonomous replication of the vector in the cell independent of the genome.
For integration into the host cell genome, the vector may rely on the polynucleotide's sequence or any other element of the vector for integration into the genome by homologous or non-homologous recombination. Alternatively, the vector may contain additional polynucleotides for directing integration by homologous recombination into the genome of the host cell at a precise location(s) in the chromosome(s). To increase the likelihood of integration at a precise location, the integrational elements should contain a sufficient number of nucleic acids, such as 100 to 10,000 base pairs, 400 to 10,000 base pairs, and 800 to 10,000 base pairs, which have a high degree of sequence identity to the corresponding target sequence to enhance the probability of homologous recombination. The integrational elements may be any sequence that is homologous with the target sequence in the genome of the host cell. Furthermore, the integrational elements may be non-encoding or encoding polynucleotides. On the other hand, the vector may be integrated into the genome of the host cell by non-homologous recombination.
For autonomous replication, the vector may further comprise an origin of replication enabling the vector to replicate autonomously in the host cell in question. The origin of replication may be any plasmid replicator mediating autonomous replication that functions in a cell. The term “origin of replication” or “plasmid replicator” means a polynucleotide that enables a plasmid or vector to replicate in vivo.
Examples of bacterial origins of replication are the origins of replication of plasmids pBR322, pUC19, pACYC177, and pACYC184 permitting replication in E. coli, and pUB110, pE194, pTA1060, and pAMß1 permitting replication in Bacillus.
Examples of origins of replication for use in a yeast host cell are the 2 micron origin of replication, ARS1, ARS4, the combination of ARS1 and CEN3, and the combination of ARS4 and CEN6.
Examples of origins of replication useful in a filamentous fungal cell are AMA1 and ANS1 (Gems et al., 1991, Gene 98: 61-67; Cullen et al., 1987, Nucleic Acids Res. 15: 9163-9175; WO 00/24883). Isolation of the AMA1 gene and construction of plasmids or vectors comprising the gene can be accomplished according to the methods disclosed in WO 00/24883.
More than one copy of a polynucleotide of the present invention may be inserted into a host cell to increase production of a polypeptide. An increase in the copy number of the polynucleotide can be obtained by integrating at least one additional copy of the sequence into the host cell genome or by including an amplifiable selectable marker gene with the polynucleotide where cells containing amplified copies of the selectable marker gene, and thereby additional copies of the polynucleotide, can be selected for by cultivating the cells in the presence of the appropriate selectable agent.
The procedures used to ligate the elements described above to construct the recombinant expression vectors of the present invention are well known to one skilled in the art (see, e.g., Sambrook et al., 1989, supra).
The present invention also relates to recombinant host cells comprising polynucleotides of the present invention operably linked to one or more control sequences that direct expression of the polynucleotides of the invention. A construct or vector comprising a polynucleotide is introduced into a host cell so that the construct or vector is maintained as a chromosomal integrant or as a self-replicating extra-chromosomal vector as described earlier. The term “host cell” encompasses any progeny of a parent cell that is not identical to the parent cell due to mutations that occur during replication.
The host cell may be any useful cell, e.g., a prokaryote or a eukaryote.
The prokaryotic host cell may be any Gram-positive or Gram-negative bacterium. Gram-positive bacteria include, but are not limited to, Bacillus, Clostridium, Enterococcus, Geobacillus, Lactobacillus, Lactococcus, Oceanobacillus, Staphylococcus, Streptococcus, and Streptomyces. Gram-negative bacteria include, but are not limited to, Campylobacter, E. coli, Flavobacterium, Fusobacterium, Helicobacter, Ilyobacter, Neisseria, Pseudomonas, Salmonella, and Ureaplasma.
The prokaryotic host cell may be any Bacillus cell including, but not limited to, Bacillus alkalophilus, Bacillus altitudinis, Bacillus amyloliquefaciens, B. amyloliquefaciens subsp. plantarum, Bacillus brevis, Bacillus circulans, Bacillus clausii, Bacillus coagulans, Bacillus firmus, Bacillus lautus, Bacillus lentus, Bacillus licheniformis, Bacillus megaterium, Bacillus methylotrophicus, Bacillus pumilus, Bacillus safensis, Bacillus stearothermophilus, Bacillus subtilis, and Bacillus thuringiensis cells. Preferably, the prokaryotic host cell is a Bacillus licheniformis cell.
The prokaryotic host cell may also be any Streptococcus cell including, but not limited to, Streptococcus equisimilis, Streptococcus pyogenes, Streptococcus uberis, and Streptococcus equi subsp. Zooepidemicus cells.
The prokaryotic host cell may also be any Streptomyces cell including, but not limited to, Streptomyces achromogenes, Streptomyces avermitilis, Streptomyces coelicolor, Streptomyces griseus, and Streptomyces lividans cells.
The introduction of DNA into a Bacillus cell may be effected by protoplast transformation (see, e.g., Chang and Cohen, 1979, Mol. Gen. Genet. 168: 111-115), competent cell transformation (see, e.g., Young and Spizizen, 1961, J. Bacteriol. 81: 823-829, or Dubnau and Davidoff-Abelson, 1971, J. Mol. Biol. 56: 209-221), electroporation (see, e.g., Shigekawa and Dower, 1988, Biotechniques 6: 742-751), or conjugation (see, e.g., Koehler and Thorne, 1987, J. Bacteriol. 169: 5271-5278). The introduction of DNA into an E. coli cell may be effected by protoplast transformation (see, e.g., Hanahan, 1983, J. Mol. Biol. 166: 557-580) or electroporation (see, e.g., Dower et al., 1988, Nucleic Acids Res. 16: 6127-6145). The introduction of DNA into a Streptomyces cell may be effected by protoplast transformation, electroporation (see, e.g., Gong et al., 2004, Folia Microbiol. (Praha) 49: 399-405), conjugation (see, e.g., Mazodier et al., 1989, J. Bacteriol. 171: 3583-3585), or transduction (see, e.g., Burke et al., 2001, Proc. Natl. Acad. Sci. USA 98: 6289-6294). The introduction of DNA into a Pseudomonas cell may be effected by electroporation (see, e.g., Choi et al., 2006, J. Microbiol. Methods 64: 391-397) or conjugation (see, e.g., Pinedo and Smets, 2005, Appl. Environ. Microbiol. 71: 51-57). The introduction of DNA into a Streptococcus cell may be effected by natural competence (see, e.g., Perry and Kuramitsu, 1981, Infect. Immun. 32: 1295-1297), protoplast transformation (see, e.g., Catt and Jollick, 1991, Microbios 68: 189-207), electroporation (see, e.g., Buckley et al., 1999, Appl. Environ. Microbiol. 65: 3800-3804), or conjugation (see, e.g., Clewell, 1981, Microbiol. Rev. 45: 409-436). However, any method known in the art for introducing DNA into a host cell can be used.
The host cell may also be a eukaryote, such as a mammalian, insect, plant, or fungal cell.
The host cell may be a fungal cell. “Fungi” as used herein includes the phyla Ascomycota, Basidiomycota, Chytridiomycota, and Zygomycota as well as the Oomycota and all mitosporic fungi (as defined by Hawksworth et al., In, Ainsworth and Bisby's Dictionary of The Fungi, 8th edition, 1995, CAB International, University Press, Cambridge, UK).
The fungal host cell may be a yeast cell. “Yeast” as used herein includes ascosporogenous yeast (Endomycetales), basidiosporogenous yeast, and yeast belonging to the Fungi imperfecti (Blastomycetes). Since the classification of yeast may change in the future, for the purposes of this invention, yeast shall be defined as described in Biology and Activities of Yeast (Skinner, Passmore, and Davenport, editors, Soc. App. Bacteriol. Symposium Series No. 9, 1980).
The yeast host cell may be a Candida, Hansenula, Kluyveromyces, Pichia, Saccharomyces, Schizosaccharomyces, or Yarrowia cell, such as a Kluyveromyces lactis, Saccharomyces carlsbergensis, Saccharomyces cerevisiae, Saccharomyces diastaticus, Saccharomyces douglasii, Saccharomyces kluyveri, Saccharomyces norbensis, Saccharomyces oviformis, or Yarrowia lipolytica cell.
The fungal host cell may be a filamentous fungal cell. “Filamentous fungi” include all filamentous forms of the subdivision Eumycota and Oomycota (as defined by Hawksworth et al., 1995, supra). The filamentous fungi are generally characterized by a mycelial wall composed of chitin, cellulose, glucan, chitosan, mannan, and other complex polysaccharides. Vegetative growth is by hyphal elongation and carbon catabolism is obligately aerobic. In contrast, vegetative growth by yeasts such as Saccharomyces cerevisiae is by budding of a unicellular thallus and carbon catabolism may be fermentative.
The filamentous fungal host cell may be an Acremonium, Aspergillus, Aureobasidium, Bjerkandera, Ceriporiopsis, Chrysosporium, Coprinus, Coriolus, Cryptococcus, Filibasidium, Fusarium, Humicola, Magnaporthe, Mucor, Myceliophthora, Neocallimastix, Neurospora, Paecilomyces, Penicillium, Phanerochaete, Phlebia, Piromyces, Pleurotus, Schizophyllum, Talaromyces, Thermoascus, Thielavia, Tolypocladium, Trametes, or Trichoderma cell.
For example, the filamentous fungal host cell may be an Aspergillus awamori, Aspergillus foetidus, Aspergillus fumigatus, Aspergillus japonicus, Aspergillus nidulans, Aspergillus niger, Aspergillus oryzae, Bjerkandera adusta, Ceriporiopsis aneirina, Ceriporiopsis caregiea, Ceriporiopsis gilvescens, Ceriporiopsis pannocinta, Ceriporiopsis rivulosa, Ceriporiopsis subrufa, Ceriporiopsis subvermispora, Chrysosporium inops, Chrysosporium keratinophilum, Chrysosporium lucknowense, Chrysosporium merdarium, Chrysosporium pannicola, Chrysosporium queenslandicum, Chrysosporium tropicum, Chrysosporium zonatum, Coprinus cinereus, Coriolus hirsutus, Fusarium bactridioides, Fusarium cerealis, Fusarium crookwellense, Fusarium culmorum, Fusarium graminearum, Fusarium graminum, Fusarium heterosporum, Fusarium negundi, Fusarium oxysporum, Fusarium reticulatum, Fusarium roseum, Fusarium sambucinum, Fusarium sarcochroum, Fusarium sporotrichioides, Fusarium sulphureum, Fusarium torulosum, Fusarium trichothecioides, Fusarium venenatum, Humicola insolens, Humicola lanuginosa, Mucor miehei, Myceliophthora thermophila, Neurospora crassa, Penicillium purpurogenum, Phanerochaete chrysosporium, Phlebia radiata, Pleurotus etyngii, Thielavia terrestris, Trametes villosa, Trametes versicolor, Trichoderma harzianum, Trichoderma koningii, Trichoderma longibrachiatum, Trichoderma reesei, or Trichoderma viride cell.
Fungal cells may be transformed by a process involving protoplast formation, transformation of the protoplasts, and regeneration of the cell wall in a manner known per se. Suitable procedures for transformation of Aspergillus and Trichoderma host cells are described in EP 238023, Yelton et al., 1984, Proc. Natl. Acad. Sci. USA 81: 1470-1474, and Christensen et al., 1988, Bio/Technology 6: 1419-1422. Suitable methods for transforming Fusarium species are described by Malardier et al., 1989, Gene 78: 147-156, and WO 96/00787. Yeast may be transformed using the procedures described by Becker and Guarente, In Abelson, J. N. and Simon, M. I., editors, Guide to Yeast Genetics and Molecular Biology, Methods in Enzymology, Volume 194, pp 182-187, Academic Press, Inc., New York; Ito et al., 1983, J. Bacteriol. 153: 163; and Hinnen et al., 1978, Proc. Natl. Acad. Sci. USA 75: 1920.
Several RNA-guided endonucleases are known, and more are being discovered as the scientific interest has increased over the last few years; a review is provided in Makarova et al., 2015, An updated evolutionary classification of CRISPR-Cas systems, Nature 13: 722-736.
Nuclease-null variants of the RNA-guided endonuclease of Eubacterium rectale (SEQ ID NO: 2, known as Mad7) may be prepared by disrupting its endonuclease activity, e.g., by introducing loss-of-function mutations in the catalytic domain responsible for endonuclease activity.
In an embodiment, the RNA-guided endonuclease has a sequence identity of at least 60%, e.g., at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100%, to SEQ ID NO: 2; preferably the RNA-guided endonuclease comprises or consists of SEQ ID NO: 2.
In an embodiment, the polynucleotide encoding the RNA-guided endonuclease has a sequence identity of at least 60%, e.g., at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100%, to SEQ ID NO: 1; preferably the polynucleotide comprises or consists of SEQ ID NO: 1.
In an embodiment, the nuclease-null variant of an RNA-guided endonuclease has a sequence identity of at least 60%, e.g., at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, but less than 100%, to SEQ ID NO: 2, and comprises an alteration of an amino acid at a position corresponding to position 877 of SEQ ID NO: 2. In a preferred embodiment, the amino acid at a position corresponding to position 877 of SEQ ID NO: 2 is substituted with Ala, Arg, Asn, Asp, Cys, Gln, Glu, Gly, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, or Val, preferably with Ala. In a preferred embodiment, the nuclease-null variant comprises or consists of the substitution D877A of SEQ ID NO: 2.
The gRNA in CRISPR genome editing constitutes the re-programmable part that makes the system so versatile. In the natural S. pyogenes system, the gRNA is actually a complex of two RNA polynucleotides, a first crRNA containing about 20 nucleotides that determine the specificity of the RNA-guided endonuclease known as Cas9 and the tracr RNA which hybridizes to the crRNA to form an RNA complex that interacts with Cas9 (see Jinek et al., 2012, A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity, Science 337: 816-821). The terms crRNA and tracrRNA are used interchangeably with the terms tracr-mate RNA and tracr RNA herein.
Since the discovery of the CRISPR-Cas9 system single polynucleotide gRNAs have been developed and successfully applied just as effectively as the natural two-part gRNA complex.
In a preferred embodiment, the gRNA or the at least two gRNA comprise a first RNA comprising 20 or more nucleotides (e.g., 21, 22, 23, 24, or 25 nucleotides) that are at least 85% complementary to and capable of hybridizing to the polynucleotide(s) encoding the selectable marker(s); preferably the 20 or more nucleotides (e.g., 21, 22, 23, 24, or 25 nucleotides) are at least 90%, 95%, 97%, 98%, 99% or even 100% complementary to and capable of hybridizing to the polynucleotide(s) encoding the selectable marker(s).
In a particularly preferred embodiment, the gRNA or the at least two gRNA comprise a first RNA comprising 21 nucleotides that are at least 85% complementary to and capable of hybridizing to the polynucleotide(s) encoding the selectable marker(s); preferably the 21 nucleotides are at least 90%, 95%, 97%, 98%, 99% or even 100% complementary to and capable of hybridizing to the polynucleotide(s) encoding the selectable marker(s).
In a preferred embodiment, a host cell of the invention comprises a single gRNA comprising the first and second RNAs in the form of a single polynucleotide and wherein the tracr mate sequence and the tracr sequence form a stem-loop structure when hybridized with each other.
In order for an RNA-guided endonuclease-gRNA complex to be capable of hybridizing to a target sequence, such as the polynucleotide(s) encoding the selectable marker(s), the target sequence should be flanked by a functional protospacer adjacent motif (PAM sequence) for that particular RNA-guided endonuclease. For an overview of PAM sequences, see, for example, Shah et al, 2013, Protospacer recognition motifs, RNA Biol. 10 (5): 891-899.
In a preferred embodiment, the PAM sequence is TTTN; more preferably, the PAM sequence is selected from the group consisting of TTTA, TTTT, TTTG, and TTTC; most preferably the PAM sequence is TTTC.
The present invention is further described by the following examples that should not be construed as limiting to the scope of the invention.
Chemicals used as buffers and substrates are commercial products of at least reagent grade.
PCR amplifications are performed using standard textbook procedures, employing a commercial thermocycler and either Ready-To-Go PCR beads, Phusion polymerase, or RED-TAQ polymerase from commercial suppliers.
LB agar: See EP 0 506 780.
LBPSG agar plates contains LB agar supplemented with phosphate (0.01 M K3PO4), glucose (0.4%), and starch (0.5%); See EP 0 805 867 B1.
TY (liquid broth) medium: See WO 1994/14968, p 16.
Oligonucleotide primers are obtained from DNA technology, Aarhus, Denmark. DNA manipulations (plasmid and genomic DNA preparation, restriction digestion, purification, ligation, DNA sequencing) are performed using standard textbook procedures with commercially available kits and reagents.
TSS medium: 450 ml Millipore-purified water containing 10 g Bacto agar is autoclaved for 20 min. After cooling to approx. 60 ° C., the following ingredients are added: 25 ml 1M Tris pH 7.5, 1 ml 2% FeCl3 6H2O, 1 ml 2% trisodium citrate dehydrate, 1.25 ml 1 M K2HPO4, 1 ml 10% MgSO4 7H2O, 10 ml 10% L-glutamine (L-glutamine is only solubilized during heating and autoclaving), and 1.9 ml 87% glycerol to get 0.4% in 430 ml.
Ligation mixtures are in some cases amplified in an isothermal rolling circle amplification reaction, using the TempliPhi kit from GE Healthcare.
DNA is introduced into B. subtilis rendered naturally competent, either using a two-step procedure (Yasbin et al., 1975, J. Bacteriol. 121: 296-304), or a one-step procedure, in which cell material from an agar plate is resuspended in Spizisen 1 medium (WO 2014/052630), 12 ml is shaken at 200 rpm for approx. 4 hours at 37° C., DNA is added to 400 microliter aliquots, and these are further shaken 150 rpm for 1 hour at the desired temperature before plating on selective agar plates.
DNA is introduced into B. licheniformis by conjugation from B. subtilis, essentially as previously described (EP 2 029 732 B1), using a modified B. subtilis donor strain PP3724, containing pLS20, wherein the methylase gene M.bli1904II (US 2013/0177942) is expressed from a triple promoter at the amyE locus, the pBC16-derived orf beta and the B. subtilis comS gene (and a kanamycin resistance gene) are expressed from a triple promoter at the alr locus (making the strain D-alanine requiring), and the B. subtilis comS gene (and a cat gene) are expressed from a triple promoter at the pel locus.
B. subtilis JA1343: JA1343 is a sporulation negative derivative of PL1801 (WO 2005/042750). Part of the gene spolIAC has been deleted to obtain the sporulation negative phenotype.
All of the constructions described in the examples are assembled from synthetic DNA fragments ordered from GeneArt—ThermoFisher Scientific. The fragments are assembled by sequence overlap extension (SOE) as described in the examples.
The temperature-sensitive plasmids used in this patent re incorporated into the genome of B. licheniformis by chromosomal integration and excision according to the method previously described (U.S. Pat. No. 5,843,720). B. licheniformis transformants containing plasmids are grown on LBPG selective medium with erythromycin at 50° C. to force integration of the vector at identical sequences of the chromosome. Desired integrants are chosen based on their ability to grow on LBPG+erythromycin selective medium at 50° C. Integrants are then grown without selection in LBPG medium at 37° C. to allow excision of the integrated plasmid. Cells are plated on LBPG plates and screened for erythromycin-sensitivity. The sensitive clones are checked for correct integration of the desired construct.
PP3724: B. subtilis stain containing pLS20, wherein the methylase gene M.bli1904II (US 2013/0177942) is expressed from a triple promoter at the amyE locus, the pBC16-derived orf beta and the B. subtilis comS gene (and a kanamycin resistance gene) are expressed from a triple promoter at the alr locus (making the strain D-alanine requiring), and the B. subtilis comS gene (and a cat gene) are expressed from a triple promoter at the pel locus.
JA1622: This strain is the B. subtilis 168 derivative JA578 described in WO 2002/00907 with a disrupted spolIAC gene (sigF). The genotype is: amyE::repF (pE194), spolIAC.
SJ1904: This strain is a B. licheniformis strain described in WO 2008/066931. The gene encoding the alkaline protease (aprL) is inactivated.
PP3811: A derivative of B. licheniformis strain SJ1904, where the alkaline protease gene aprL, metalloprotease mprL, and the spolIAC gene is inactivated.
PP3811-Mad7d: This strain is the B. licheniformis strain PP3811 where the mad7d gene is inserted at the bglC locus. The final insert has the mad7d gene transcribed from the PamyL promoter variant described in WO 1993/010249. The final sequence on the chromosome after integration is described in
PP3811-Mad7gDNA1: This strain is the B. licheniformis strain PP3811-Mad7d where the dsRED gene and a gDNA(cat) transcribing the gRNA(cat) directed against the catL gene in B. licheniformis is inserted into the gnt locus. Further downstream of gDNA the attB site from phage TP901-1 is positioned (WO 2006/042548). The dsRED gene is expressed from the triple promoter described in WO 1999/043835. The final sequence on the chromosome after integration is described in
PP3811-Mad7gDNA2: This strain is the B. licheniformis strain PP3811-Mad7gDNA1 where the dsRED gene and a gDNA(cat) transcribing the gRNA(cat) directed against the catL gene in B. licheniformis is inserted into the amyL locus. Further downstream of gDNA the attB site is positioned (see above). The final sequence on the chromosome after integration is described in
PP3811-Mad7gDNA3: This strain is the B. licheniformis PP3811-Mad7gDNA2 where the dsRED gene and a gDNA(cat) transcribing the gRNA(cat) directed against the catL gene in B. licheniformis is inserted into the lacA2 locus. Further downstream of gDNA the attB site is positioned (see above). The final sequence on the chromosome after integration is described in
MOL7800-amyL3: This is the B. licheniformis strain PP3811-Mad7gDNA3 where the three copies of dsRED gene and gDNA(cat) is replaced with three copies of the amyL gene encoding the alpha-amylase from B. licheniformis. The final sequence of the three loci of the chromosome after replacement is described in
PP3724-pPPamyL-attP: This strain is the conjugation donor strain PP3724 holding the plasmid pPPamyL-attP.
pC194: Plasmid isolated from Staphylococcus aureus (Horinouchi and Weisblum, 1982).
pE194: Plasmid isolated from S. aureus (Horinouchi and Weisblum, 1982).
pUB110: Plasmid isolated from S. aureus (McKenzie et al., 1986)
pPPamyL-attP: Plasmid constructed for this invention in Example 6. The plasmid was made by assembly of synthetic sequences to generate a vector holding the: (1) amyL gene encoding the alpha-amylase from B. licheniformis preceded by the cry3A stabilizer for integration (2) the attP and the integrase (int) from TP901-1 described in WO 2006/042548. The integrase promote integration between the attP site on the plasmid and the attB site on the chromosome of the B. licheniformis host.
An expression cassette is inserted at the bglC locus where the mad7d gene encoding a nuclease-null variant of SEQ ID NO: 2 (Mad7d, comprising the D877A substitution) is expressed from the amyL promoter (P4199) described in WO 1993/010249.
The DNA for integration is ordered as synthetic DNA (GeneArt-ThermoFisher Scientific) and cloned into integration vectors as earlier described in WO 2006/042548. The final map of the bglC locus is shown in
The condition for the PCR amplifications is as follows: The respective DNA fragments are amplified by PCR using the Phusion Hot Start DNA Polymerase system (Thermo Scientific). The PCR amplification reaction mixture contains 1 ul (˜0.1 ug) of template DNA, 2 ul of sense primer (20 pmol/ul), 2 ul of anti-sense primer (20 pmol/ul), 10 ul of 5×PCR buffer with 7.5 mM MgCl2, 8 ul of dNTP mix (1.25 mM each), 37 ul water, and 0.5 ul (2 U/ul) DNA polymerase mix. A thermocycler is used to amplify the fragment. The PCR products are purified from a 1.2% agarose gel with 1×TBE buffer using the Qiagen QIAquick Gel Extraction Kit (Qiagen, Inc., Valencia, Calif.) according to the manufacturer's instructions.
The PCR products are used in subsequent PCR reactions to create a single plasmid using splice overlapping PCR (SOE) using the Phusion Hot Start DNA Polymerase system (Thermo Scientific). The PCR amplification reaction mixture contains 50 ng of each of the two gel-purified PCR products and the synthetic fragment and a thermocycler is used to assemble and amplify the plasmid. The resulting SOE product is used directly for transformation of B. subtilis host JA1622 to establish the plasmid. The plasmid is transferred by competence to the donor strain PP3724.
This recipient B. licheniformis strain is transformed with the plasmid described above and integrated and excised according to the procedure described above. By this procedure, the bglC locus on the chromosome is replaced with the cloned construct delivered by the plasmid (
An expression cassette is inserted at the gnt locus where the dsRED marker gene encoding the red fluorescent protein is expressed from the P3 promoter described in WO 2005/098016. Downstream of the dsRED marker gene, a Mad7gDNA sequence is expressed from the amyQ promoter from B. amyloliquefaciens. The gDNA transcribes a gRNA directed against the cat marker gene. The cat marker gene encodes an acetyl transferase from B. licheniformis which confer resistance to chloramphenicol. The chromosomal integration of DNA into B. licheniformis has been described in WO 2007/138049. The DNA for integration is ordered as synthetic DNA (GeneArt-ThermoFisher Scientific), assembled by SOE-PCR, and cloned into temperature-sensitive integration vectors based on pE194 as earlier described. The final map of the gnt locus is shown in
The PCR products are made as described in Example 1 and used in a subsequent PCR reaction to create a single plasmid using splice overlapping PCR (SOE) using the Phusion Hot Start DNA Polymerase system (Thermo Scientific). The PCR amplification reaction mixture contains 50 ng of each of the two gel purified PCR products and the synthetic fragment and a thermocycler is used to assemble and amplify the integration plasmid. The resulting SOE product is used directly for transformation of B. subtilis host JA1622 to establish the integration plasmid. The plasmid is transferred to the donor strain PP3724 and used for conjugation. The plasmid is used to insert the dsRED gene and the Mad7gDNA(cat) at the gnt locus of B. licheniformis according to the procedure described in Example 1. The final strain is named PP3811-Mad7gDNA1.
An expression cassette identical to the one described in Example 2 is inserted at the amyL locus. The DNA for integration is ordered as synthetic DNA (GeneArt-ThermoFisher Scientific), assembled by SOE-PCR, and cloned into temperature-sensitive integration vectors based on pE194 as earlier described in WO 2006/042548. The final map of the amyL locus is shown in
The PCR products are made as described in Example 1 and used in a subsequent PCR reaction to create a single plasmid using splice overlapping PCR (SOE) using the Phusion Hot Start DNA Polymerase system (Thermo Scientific). The PCR amplification reaction mixture contains 50 ng of each of the two gel purified PCR products and the synthetic fragment and a thermocycler is used to assemble and amplify the integration plasmid. The resulting SOE product is used directly for transformation of B. subtilis host JA1622 to establish the integration plasmid. This plasmid is used to insert the dsRED gene and the Mad7gDNA(cat) at the amyL locus of B. licheniformis strain PP3811-Mad7gDNA1 as described above in Example 2. The final strain is named PP3811-Mad7gDNA2. This strain has two copies of Mad7gDNA(cat) encoding gRNA directed against the catL gene in the B. licheniformis host.
An expression cassette almost identical to the ones described in Examples 2 and 3 is inserted at the lacA2 locus. The only difference is an alternative synthetic sequence of the dsRED gene (dsREDsyn). This gene variant still encodes the same fluorescent protein. The DNA for integration is ordered as synthetic DNA (GeneArt—ThermoFisher Scientific) and cloned into integration vectors as described in WO 2006/042548. The final map of the lacA2 locus is shown in
The PCR products are made as described in Example 1 and used in a subsequent PCR reaction to create a single plasmid using splice overlapping PCR (SOE) using the Phusion Hot Start DNA Polymerase system (Thermo Scientific). The PCR amplification reaction mixture contains 50 ng of each of the two gel purified PCR products and the synthetic fragment and a thermocycler is used to assemble and amplify the integration plasmid. The resulting SOE product is used directly for transformation of B. subtilis host JA1622 to establish the integration plasmid. This plasmid is used to insert the dsRED gene (dsREDsyn) and the Mad7gDNA(cat) at the lacA2 locus of B. licheniformis PP3811-Mad7gDNA2 as described above in Example 3. The final strain is named PP3811-Mad7gDNA3 and has three copies of the dsRED gene and three copies of the Mad7gDNA(cat) cassette and Mad7d expressed from the bglC locus (
The plasmid pPPamyL-attP is assembled from DNA sequences ordered from GeneArt. The entire plasmid and its annotations is depicted in
The condition for the PCR amplifications is as described in Example 1. The purified PCR products are used in a subsequent PCR reaction to create a single plasmid using splice overlapping PCR (SOE) using the Phusion Hot Start DNA Polymerase system (Thermo Scientific). The PCR amplification reaction mixture contains 50 ng of each of the six gel purified PCR products and a thermocycler is used to assemble and amplify the plasmid of 9550 bp (
The plasmid encodes the amylase gene amyL from B. licheniformis flanked upstream by the cry3A stabilizer region and the attP phage integration site.
The integration of the amyL into the chromosome will take place between the cry3A stabilizer regions present in the host strain PP3811-Mad7gDNA3 and on the plasmid and the attB and attP sites on the chromosome and plasmid respectively.
The plasmid pPPamyL-attP described in Example 5 is transformed into the B. licheniformis strain PP3811-Mad7gDNA3 to select for on-step integration of the amyL expression cassette in three different loci, gnt:dsRED-Mad7gDNA(cat), amyL:dsRED-Mad7gDNA(cat), and lacA2:dsRED-Mad7gDNA(cat). In this step, the gDNA(cat) and the dsRED gene is replaced by the amyL expression cassette. The replacement is mediated by the recombination between flanking regions on the gDNA loci on the chromosome and the introduced plasmid; upstream by the identical cry3A stabilizer regions present on the chromosome of the host strain PP3811-Mad7gDNA3 and on the plasmid pPPamyL-attP, and downstream by the attB and attP sites on the chromosome and plasmid, respectively.
After plasmid transformation of the PP3811-Mad7gDNA3, the cells are plated for three days on LBPG plates with 1 ug/ml of erythromycin at 34° C. to allow amplification and recombination events to occur between the chromosome and the plasmid at permissive temperature. The colonies are washed of in 200 ul TY and 50 ul is transferred to 5 ml of liquid cultures in TY and incubated at 200 rpm at 34° C. for 24 hours. The culture is streaked on LBPG plates with 6 ug/ml chloramphenicol (cam) to select for strains where all three gDNA(cat) loci are replaced with the amyL expression cassette.
Approx. ten different colonies from the cam plates are re-streaked and tested for amyL integration in all three loci. All colonies show the expected bands on an agarose gel.
The chloramphenicol resistant clones have amylase activity shown by plating on LBPG plates supplemented with starch. All colonies show significant halos on plates supplemented with starch verifying expression of amylase.
This example shows that the present invention can very efficiently be employed as a tool to select for integration of at least three copies of an expression cassette on the chromosome of B. licheniformis.
Examples 7 and 8 of PCT/EP2018/084463 describe the construction and utilization of a host strain for selection for genomic integration of three copies of a gene of interest. The present invention discloses an alternative and improved system for selection for integration of genes of interest. Here, a host strain is constructed that harbours a strong promoter (the triple promoter, P3), reading into a segment consisting of an FRT-F site, Mad7d together with a gDNA encoding a gRNA targeting the glpD gene, optionally a marker gene, and an FRT-F3 site. The expression of Mad7d together with the glpD-directing gRNA ensures repression of the glpD gene, resulting in a host strain unable to grow on minimal media with glycerol as sole carbon source. Other genes involved in sugar metabolism may be used as targets, with some examples being disclosed in WO 2003/055967.
The flp/FRT system (WO 2018/077796) is subsequently used to replace the Mad7d-gRNA_glpD-marker segment with a gene of interest, resulting in a strain which is now able to grow on minimal media with glycerol as sole carbon source, and the gene replacement can be selected for in this manner.
If the Mad7d-gRNA_glpD segment has been inserted into more than one chromosomal site, the selection for growth on minimal media with glycerol will result in strains where integration of the gene of interest has taken place at all such sites.
As first step in the construction, a DNA sequence consisting of an FRT-F site, a segment encoding Mad7d preceded by a ribosome binding site, a segment encoding green fluorescent protein (GFP), the PamyQsc promoter, and Mad7 scaffold and gDNA targeting the PamyL4199 variant of the amyL promoter, and an FRT-F3 site, was provided from GeneArt on an E. coli plasmid as full gene synthesis, and this plasmid was introduced into and saved in E. coli TOP10 cells, as SJ14411 (E. coli TOP10/pSJ14411). The full DNA sequence of plasmid pSJ14411 is provided here as SEQ ID NO: 11.
In a second step, three DNA sequences corresponding to part of the gfp gene, the PamyQsc promoter, and Mad7 scaffold and gDNA targeting each of three glpD gene segments, followed by an FRT-F3 site, were obtained from GeneArt on E. coli plasmids as full gene synthesis. These plasmids were introduced into and saved in E. coli TOP10 cells, as SJ14412 (E. coli TOP10/pSJ14412), SJ14413 (E. coli TOP10/pSJ14413), and SJ14414 (E. coli TOP10/pSJ14414).
The full DNA sequences of plasmids pSJ14412, pSJ14413, and pSJ14414 are provided here as SEQ ID NO: 12, SEQ ID NO: 13, and SEQ ID NO: 14, respectively.
In a third step, in order to obtain the final integration constructs for the construction of host strains for selection of flp/FRT mediated chromosomal insertion, three different 3-fragment ligations were performed:
pSJ13461 (described in example 19 of WO 2018/077796) was digested with SbfI and MluI, and the 5785 bp SbfI-MluI fragment was gel-purified.
pSJ14411 was digested with MluI and MfeI, and the 4465 bp MluI-MfeI fragment was gel purified.
Each of pSJ14412, pSJ14413, and pSJ14414 were digested with MfeI and SbfI, and the 373 bp MfeI-SbfI fragment was purified from each.
Each of the pSJ14412, pSJ14413, and pSJ14414 fragments were combined with the pSJ13461 and the pSJ14411 fragments, ligated, and the ligation mixture treated with TempliPhi before introduction into B. subtilis PP3724 competent cells. The resulting transformants were pooled separately from each transformation, and these transformant pools saved as SJ14438 (PP3724/pSJ14438), SJ14439 (PP3724/pSJ14439), and SJ14440 (PP3724/pSJ14440).
The full DNA sequences of plasmids pSJ14438, pSJ14439, and pSJ14440 are provided here as SEQ ID NO: 15, SEQ ID NO: 16, and SEQ ID NO: 17, respectively.
In a fourth step, the final integration constructs for construction of host strains for selection of gene integration will be introduced into a one-copy flp/FRT host strain, SJ13872 (which has a gene encoding yellow fluorescent protein (YFP) between FRT-F and FRT-F3 sites), or into a derivative which will have the YFP encoding gene exchanged with a red fluorescent protein (RFP) encoding gene. To bring about this color gene exchange, a temperature sensitive vector expressing flippase and carrying the segment FRT-F-RFP-FRT-F3 was constructed, introduced into B. subtilis PP3724, and saved as SJ14491 (pSJ14491/PP3724), for subsequent conjugation into B. licheniformis SJ13872. The full DNA sequence of pSJ14491 is provided here, as SEQ ID NO: 18.
pSJ14491 will be introduced into SJ13872 by conjugation, with transconjugants being selected on LBPSG agar plates with erythromycin (2 microgram/ml). These transconjugants are further plated to single colonies on plates without erythromycin, and those that seem to have the lost the plasmid (being erythromycin sensitive) and show red fluorescence, indicating that RFP has replaced YFP, are kept.
The one-copy flp/FRT host strain used here, SJ13872, was developed from SJ1904 (a B. licheniformis strain described in WO 2008/066931) and contains at the chromosomal lacA2 locus the P3 promoter reading into a segment consisting of FRT-F, a gene encoding YFP, and FRT-F3. Strain SJ13872 is wildtype with respect to the glpD locus but contains a number of other modifications that are irrelevant with respect to its use as described in the present application.
The three different plasmids pSJ14438, pSJ14439, and pSJ14440, carrying three separate gDNAs encoding gRNAs targeting different segments of the B. licheniformis glpD gene, are introduced by conjugation into SJ13872 or into its red derivative. Transconjugants are selected on LBPSG agar plates with erythromycin (2 microgram/ml) at 30° C. These transconjugants are further plated to single colonies on plates without erythromycin, and those that seem to have the lost the plasmid (being erythromycin sensitive) and are showing green fluorescence, are kept.
These transconjugant colonies are further plated on TSS minimal media plates with glycerol as sole carbon source to verify that they are unable to grow on such plates (due to expression of Mad7d and gRNA_glpD, which represses glpD expression).
When, however, the strains derived from either SJ13872 or its red derivative by integration of the Mad7d+gRNA_glpD constructs are used as recipients in conjugations with donor strains that carry, e.g., a gene of interest like the amyL gene, between FRT-F and FRT-F3 sites on a vector also expressing flippase, transconjugants can be selected as before on LBPSG agar plates containing erythromycin (2 microgram/ml), and strains in which the Mad7d+gRNA_glpD segment is replaced by the gene of interest (e.g., amyL) can be directly selected for by their ability to grow on/in TSS minimal medium with glycerol as sole carbon source.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19182334.3 | Jun 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/066557 | 6/16/2020 | WO |
