Regulatory gene for the expression of nitrile hydratase gene

FIELD OF THE INVENTION
The present invention relates to a regulatory gene derived from bacteria of the genus Rhodococcus and coding for a polypeptide capable of activating a promoter for a nitrile hydratase gene, a recombinant DNA containing said DNA, and a transformant transformed with said recombinant DNA.
BACKGROUND OF THE INVENTION
Processes for producing amides by nitrile hydratase that is an enzyme hydrating nitriles to amides came to be used as industrially advantageous methods by virtue of the reaction at normal temperature and pressure, higher conversion degree, etc. In particular, bacteria of the genus Rhodococcus are known to accumulate a significant amount of the enzyme in their cells to exhibit high catalytic activity (see Japanese Patent Publication No. 4873/1992 and Japanese Laid-Open Patent Publication Nos. 91189/1987, 470/1990 and 84198/1990).
As compared with such conventional processes, those using a nitrile hydratase gene cloned by genetic recombination are expected to attain drastic improvements in the catalytic ability of bacteria to hydrate nitriles because the bacteria can be engineered to contain multiple copies of the same gene. Further improvements in the enzyme are also facilitated by genetic recombination techniques such as site-specific mutagenesis, random mutagenesis, etc. A nitrile hydratase gene derived from the genus Rhodococcus has been obtained from N-774 (Japanese Laid-Open Patent Publication No. 119778/1990) and J-1 (Japanese Laid-Open Patent Publication No. 211379/1992). The nitrile hydratase gene from N-774 could successfully inserted into a Rhodococcus--E. coli hybrid plasmid vector (Japanese Laid-Open Patent Publication No. 64589/1993) and attained high activity when introduced into bacteria of the genus Rhodococcus (Japanese Laid-Open Patent Publication No. 68566/1993). On the other hand, there is no report on the expression of the nitrile hydratase gene derived from Rhodococcus rhodochrous J-1 in bacteria of the genus Rhodococcus, in spite of its higher nitrile hydratase activity than N-774.
SUMMARY OF THE INVENTION
The present inventors speculated that the failure to express the gene derived from J-1 results from the absence in the DNA fragment of a regulatory gene involved in function of a promoter for the nitrile hydratase gene. Hence, they sought for the regulatory gene in total DNA from J-1 and found the gene located upstream of the nitrile hydratase structural gene. This gene was successfully used for the high-level expression of nitrile hydratase in a transformant of the genus Rhodococcus.
That is, the present invention relates to a regulatory gene derived from bacteria of the genus Rhodococcus and coding for a polypeptide capable of activating a promoter for the nitrile hydratase gene, a recombinant DNA containing said DNA, and a transformant transformed with said recombinant DNA.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the construction scheme of the recombinant plasmid pHJK18.
FIG. 2 shows the construction scheme of the recombinant plasmid pHJK19.

DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention is described in detail. The present invention is practiced in the following steps.
(1) Preparation of chromosomal DNA
Total DNA is isolated from Rhodococcus rhodochrous J-1.
(2) Construction of a DNA Library
The fragment of the target nitrile hydratase gene is excised from a plasmid containing the nitrile hydratase gene from J-1 and then labeled with a radioisotope. This fragment is used as a probe.
The total DNA obtained in step (1) is cleaved with restriction enzymes and subjected to Southern hybridization (Southern E. M., J. Mol. Biol. 98, 503 (1975)) with the probe prepared above. The detected DNA fragments containing the target gene are inserted into a plasmid vector pUC19 to prepare a library.
(3) Preparation of transformants and selection of a recombinant DNA
The recombinant DNA library constructed in step (2) is used for preparation of transformants from which a colony carrying the target recombinant DNA is selected by colony hybridization (R. Bruce Wallace et al., Nuc. Acids Res. 9, 879 (1981)) using the probe obtained in step (2). The hybridized colony is further subjected to Southern hybridization so that the presence of the target recombinant DNA is confirmed.
(4) Isolation and purification of a recombinant plasmid and construction of a restriction enzyme map
A recombinant plasmid is isolated from the transformant obtained in step (3). This plasmid is designated plasmid pNHU10. It is cleaved with various restriction enzymes and analyzed by electrophoresis to prepare a restriction enzyme map.
(5) Construction of a recombinant plasmid by inserting a fragment containing a regulatory gene and the nitrile hydratase gene into a plasmid vector capable of replicating in the genus Rhodococcus
Recombinant plasmids pHK18 and pHK19, each carrying a regulatory gene and a fragment containing a nitrile hydratase gene, are constructed by inserting the plasmid obtained in step (4) and plasmid pNHJ10H containing the nitrile hydratase gene derived from J-1 into the hybrid plasmid vector pK4.
(6) Transformation of bacteria of the genus Rhodococcus and production of nitrile hydratase by the transformant
The plasmid obtained in step (5) is introduced into bacteria of the genus Rhodococcus, and the expression of the nitrile hydratase in the transformant is confirmed.
(7) Deletion-plasmids and nitrile hydratase activity
Deletion-plasmids are prepared by deletion of various regions from the plasmid obtained in step (5). The resultant deletion-plasmids are used to identify which region is essential for the expression of nitrile hydratase. The region essential for the expression of nitrile hydratase, but not encoding nitrile hydratase, is thus identified.
(8) Nucleotide sequencing
The nucleotide sequence of the region identified in step (7) is determined.
Rhodococcus rhodochrous J-1 has been deposited as FERM BP-1478 with the National Institute of Bioscience and Human-Technology, Agency of Industrial Science and Technology, Japan. Transformant TG1/pNHJ10H (FERM BP-2777) containing plasmid pNHJ10H, transformant Rhodococcus rhodochrous ATCC12674/pK4 (FERM BP-3731) containing the hybrid plasmid vector pK4, and transformant JM109/pNHU10 (FERM BP-5224) containing plasmid pNHU10 have been deposited as substitutes for plasmid pNHJ10H, hybrid plasmid vector pK4, and plasmid pNHU10, respectively.
EFFECT OF THE INVENTION
The introduction of the regulatory gene of the invention along with the nitrile hydratase gene and its promoter region permits bacteria of the genus Rhodococcus to produce a higher level of nitrile hydratase. Other extraneous gene can also be introduced into a region downstream of the promoter to produce other proteins in high yield.
PREFERRED EMBODIMENTS OF THE INVENTION
Hereinafter, the present invention will be illustrated in detail by reference to the following Example, which however is not intended to limit the scope of the invention.
The following abbreviations are used in Example.
TE: 10 mM Tris-HCl (pH 7.8)-1 mM EDTA (pH 8.0)
TNE: 50 mM Tris-HCl (pH 8.0)-1 mM EDTA (pH 8.0)-50 mM NaCl
STE: 50 mM Tris-HCl (pH 8.0)-1 mM EDTA (pH 8.0)-35 mM sucrose
2.sup.X YT medium: 1.6% trypton, 1% yeast extract, 0.5% NaCl
MY medium: 1% polypeptone, 0.3% yeast extract, 0.3% malt extract, 1% glucose
(1) Preparation of total DNA
Rhodococcus rhodochrous J-1 (FERM BP-1478) was incubated at 28.degree. C. for 2 days in 100 ml medium (glucose, KH.sub.2 PO.sub.4, K.sub.2 HPO.sub.4, MgSO.sub.4.7H.sub.2 O, yeast extract, peptone, CoCl.sub.2, urea, 1L water, pH 7.2). The bacterial cells were harvested by centrifugation and the pellet was washed with TNE and suspended in 10 ml TE. 4 ml of 0.25M EDTA, 10-20 mg lysozyme, 10-20 mg achromoprotease and 10 ml of 10% SDS were added to the suspension. The suspension was allowed to stand at 37.degree. C. for 3 hours and then centrifuged. 0.7 ml of 2.5M sodium acetate and diethyl ether were added to 20 ml of the supernatant. The upper layer was discarded, and 2 volumes of ethanol was added to the lower layer. The DNA precipitates were recovered with a grass rod. The DNA was rinsed for 5 minutes each with TE:ethanol 2:1, 1:9 and 0:10 (v/v) and then dissolved in 2-4 ml TE. 10 .mu.l of a mixture of RNase A and T1 was added to the solution and the mixture was incubated at 37.degree. C. An equal amount of TE-saturated phenol was added to the mixture which was then centrifuged. More than equal amount of ether was added to the upper layer, and the lower layer was saved. The lower layer was dialyzed overnight against 2L TE containing a small amount of chloroform and further dialyzed for 3-4 hours against fresh TE buffer. 4 ml of crude total DNA was obtained.
(2) Construction of a DNA library
10 .mu.l of plasmid pNHJ10H in which a 6.0 kb DNA fragment containing the H-type nitrile hydratase gene from J-1 had been inserted into vector pUC19 (Japanese Laid-Open Patent Publication No. 211379/1992; Biochim. Biophys. Acta 1129, 23-33 (1991)) was cleaved at 37.degree. C. for 2 hours with a mixture of 2 .mu.l each of restriction enzymes Sac I and Eco RI, 3 .mu.l of reaction buffer (10.sup.X) and 13 .mu.l sterilized water, and the digest was electrophoresed on 1% agarose gel. The Sac I-Eco RI fragment, 0.37 kb long, was cut off from the gel and labeled with radioisotope .sup.32 P.
The total DNA from J-1 obtained in step (1) was digested with Eco RI and Eco RV, electrophoresed on an agarose gel and subjected to Southern hybridization where the 0.37 kb Sac I-Eco RI fragment prepared above was used as the probe. An about 4.3 kb DNA fragment containing a region upstream from the nitrile hydratase gene was hybridized with the probe. A fraction containing the 4.3 kb DNA fragment was eluted from the agarose gel.
Separately, 10 .mu.l plasmid vector pUC19 was digested at 30.degree. C. for 2 hours with a mixture of 2 .mu.l each of restriction enzymes Sma I and Eco RI, 3 .mu.l reaction buffer (10.sup.X), and 13 .mu.l sterilized water. The Sma I- and Eco RI-cleaved pUC19 was purified as follows: After an equal amount of TE-saturated phenol was added to the reaction solution, the solution was stirred and separated into upper (aqueous) and lower layers by centrifugation. The upper layer was extracted again with TE-saturated phenol in the same manner and further extracted twice with an equal amount of chloroform in the same manner. 3 .mu.l of 3M sodium acetate and 90 .mu.l ethanol were added to the upper layer, and the sample was allowed to stand at -80.degree. C. for 30 minutes, centrifuged, dried and dissolved in TE.
A DNA library was prepared by inserting 3 .mu.l of the above fraction containing the 4.3 kb fragment from the total DNA into the above Sma I- and Eco RI-cleaved pUC19 by the action of TAKARA ligation kit overnight at 4.degree. C.
(3) Preparation of transformants and selection of a recombinant DNA
E. coli JM109 (available from Takara Shuzo Co., Ltd.) was inoculated into 10 ml of 2.sup.X YT medium and incubated at 37.degree. C. for 12 hours. After incubation, the resultant culture inoculated into fresh 2.sup.X YT medium to a concentration of 1%, and the mixture was incubated for 2 hours. The culture was centrifuged and the pellet was suspended in 5 ml of cold 50 mM CaCl.sub.2. The suspension was placed on ice for 40 minutes and then centrifuged again, the pellet was suspended in 0.25 ml of cold 50 mM CaCl.sub.2. 60 .mu.l of the recombinant plasmids (DNA library) prepared in step (2) was added to the suspension. The mixture was allowed to stand at 0.degree. C. for 40 minutes and heat-shocked at 42.degree. C. for 2 minutes, followed by addition of 1 ml of 2.sup.X YT medium. The mixture was incubated at 37.degree. C. for 60 minutes with shaking. The culture, 100 .mu.l per plate, was spreaded on a 2.sup.X YT agar plate containing 50 .mu.g/ml ampicillin. The plate was incubated at 37.degree. C. The colonies grown on the plate were selected for those carrying a DNA fragment upstream of the nitrile hydratase gene by colony hybridization in the following manner. The colonies grown on the plate were transferred to a nitrocellulose filter and the bacteria were lysed. The DNA was fixed on the filter and hybridized with the probe (0.37 kb fragment) obtained in step (2). The filter was autoradiographed and a colony containing the target recombinant DNA was selected. Additionally, the recombinant plasmid was extracted from the colony, and the Southern hybridization of the recombinant plasmid with the above probe indicated that the selected colony was a transformant carrying the target gene.
(4) Isolation and purification of the recombinant plasmid and construction of a restriction enzyme map
The transformant selected in step (3) was incubated at 37.degree. C. overnight in 100 ml of 2.sup.X YT medium, then collected and washed with TNE. 8 ml of STE and 10 mg lysozyme were added to the cells. The mixture was allowed to stand at 0.degree. C. for 5 minutes. 4 ml of 0.25M EDTA, 2 ml of 10% SDS (at room temperature) and 5 ml of 5M NaCl were added to the mixture. The mixture was allowed to stand at 0.degree. to 4.degree. C. for 3 hours and ultracentrifuged. 1/2 volume of 30% PEG 6000 was added to the supernatant. The mixture was allowed to stand at 0.degree. to 4.degree. C. overnight and centrifuged again. TNE was added to the pellet to bring the volume up to 7.5 ml. CsCl was added to the suspension and centrifuged to remove proteins. Then, 300-500 mg/ml ethidium bromide was added to the supernatant and the mixture was transferred to a centrifuge tube. The tube was heat-sealed and ultracentrifuged. cccDNA was recovered. More than equal amount of isopropyl alcohol saturated with water was added to cccDNA to remove the ethidium bromide. The DNA sample was dialyzed against TE, resulting in about 3 ml of the purified recombinant plasmid. The recombinant plasmid thus obtained was designated pNHU10. This recombinant plasmid was digested with several restriction enzymes, and the restriction enzyme map thus prepared is shown in FIG. 1.
(5) Construction of a recombinant plasmid by inserting a fragment containing a regulatory gene and the nitrile hydratase gene into a plasmid vector capable of replicating in the genus Rhodococcus
Plasmid pNHU10 obtained in step (4) overlapped with 0.37 kb nucleotides, and further contained 3.9 kb nucleotides upstream from, the nitrile hydratase gene derived from pNHJ10H. A 1.4 kb Fsp I-Eco RI fragment and a 0.9 kb Sca I-Eco RI fragment were excised from pNHU10 and inserted into the hybrid plasmid vector pK4 for E. coli--Rhodococcus bacteria to give plasmids pHJK16 and pHJK17, respectively. Plasmids pHJK18 and pHJK19 were constructed by inserting a 5.9 kb Eco RI fragment derived from pNHJ10H into plasmids pHJK16 and pHJK17, respectively. These steps are illustrated in FIGS. 1 and 2, respectively. In pHJK18 of FIG. 1, the thick arrow indicates the location and direction of the regulatory gene found in the present invention, and the thin arrow indicates the location and direction of the genes coding for 2 subunits of nitrile hydratase. In pHJK19 of FIG. 2, the thick arrow indicates the location and direction of the regulatory gene found in the present invention, and the thin arrow indicates the location and direction of the genes coding for 2 subunits of nitrile hydratase.
(6) Transformation of bacteria of the genus Rhodococcus and production of nitrile hydratase by the transformant
Rhodococcus rhodochrous ATCC12674 at the logarithmic growth phase was harvested by centrifugation, washed 3 times with ice-cold sterilized water and suspended in 15% PEG 6000 (polyethylene glycol 6000) to a final concentration of at least 10.sup.9 cells/ml. 1 .mu.g of plasmid pHK18 DNA or pHK19 DNA was mixed with 100 .mu.l of the bacterial suspension and the mixture was cooled on ice. This mixture of DNA and bacteria was introduced into a gene pulser chamber, cooled on ice and pulsed with a electrostatic capacity of 25 .mu.F, resistance of 400.OMEGA. and voltage of 20 kV/cm.
The bacterial suspension thus treated was placed on ice for 10 minutes and heated at 37.degree. C. for 5 minutes. 1 ml of MY medium was added to the suspension, which was then shaken at 28.degree. C. for 3 hours. The bacterial suspension was spreaded on an MY agar plate containing 50 .mu.g/ml kanamycin and incubated at 25.degree. C. for 2 days. The colony grown on the plate was streaked on another MY agar plate containing kanamycin, and their resistance to kanamycin was ascertained by their growth on the plate.
The resultant Rhodococcus rhodochrous transformants (Rhodococcus rhodochrous ATCC12674/pHJK18 and Rhodococcus rhodochrous ATCC12674/pHJK19) were incubated at 28.degree. C. for 2 days in a medium (10 g glycerol, 5 g peptone, 3 g yeast extract, 3 g malt extract, 1 g KH.sub.2 PO.sub.4, 1 g K.sub.2 HPO.sub.4, 0.01 g CoCl.sub.2.6H.sub.2 O, 0.75 g or 3.75 g urea (pH 7.0)/1L medium). The bacterial cells were harvested by centrifugation, and the pellet was washed with 150 mM NaCl and suspended in 0.1M HEPES-KOH buffer (pH 7.2) containing 0.35% n-butyric acid. The cells were disrupted by sonication and centrifuged to remove the cell membrane. The cell extract thus obtained was examined for nitrile hydratase activity. The enzyme assay was carried out in a reaction mixture containing 0.5 ml of 100 mM potassium phosphate buffer (pH 7.0), 1 ml of 200 mM acrylonitrile and 0.5 ml of the cell extract diluted with a suitable amount of water. The reaction was carried out at 20.degree. C. for 10 minutes and stopped by the addition of 0.2 ml of 1N HCl. The amount of acrylamide formed in the reaction mixture was determined by HPLC.
Table 1 shows the nitrile hydratase activities of the cell-free extracts from Rhodococcus rhodochrous ATCC12674/pHJK18 and Rhodococcus rhodochrous ATCC12674/pHJK19. In the table, urea is an inducer for nitrile hydratase.
TABLE 1______________________________________ nitrile hydratase activity urea (g/L)transformant 0 0.75 3.75______________________________________Rhodococcus rhodochrous 171 279 115ATCC12674/pHJK18Rhodococcus rhodochrous 180 242 104ATCC12674/pHJK19______________________________________ (unit/mg protein)
(7) Deletion plasmids and nitrile hydratase activity
Because it was estimated that region not involved in the expression of nitrile hydratase still remained in pHJK18 and pHJK19, deletion plasmids were prepared therefrom and examined for nitrile hydratase activity. The result indicated that the regulatory gene involved in the expression of the activity was located within an about 1.9 kb region between the Sca I and Acc III sites.
(8) Nucleotide sequencing
The nucleotide sequence of the region identified in step (7) was sequenced by the chain termination method (Sanger F. Science, 214, 1205-1210 (1980)) using DNA polymerase. The sequence analysis revealed the presence of a long open reading frame coding for the amino acid sequence shown in the Sequence Listing by SEQ ID: No. 1. The nucleotide sequence of the open reading frame is shown in the Sequence Listing by SEQ ID: No. 2.
__________________________________________________________________________SEQUENCE LISTING(1) GENERAL INFORMATION:(iii) NUMBER OF SEQUENCES: 2(2) INFORMATION FOR SEQ ID NO:1:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 361 base pairs(B) TYPE: amino acid(C) TOPOLOGY: linear(ii) MOLECULE TYPE: protein(iii) ORIGINAL SOURCE:(A) ORGANISM: Rhodococcus rhodochrous(B) STRAIN: J-1(xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:MetProLeuArgArgLeuAsnLeuGlyLeuValLeuProGlnSerGly51015ProSerGlyIlePheGlyProSerCysGlnAlaSerAlaGluTyrAla202530IleAspGluLeuAsnAlaGlyGlyGlyIleLeuGlyArgGluValThr354045AlaValPheValAspGlyGlyAlaAspProSerAlaValAlaAlaCys505560IleAlaAspGlnThrLysArgArgGluLeuAspAlaValValGlyTrp65707580HisThrSerAlaValArgArgArgIleValSerAlaIleGlyGlyArg859095IleProTyrValTyrThrAlaValTyrGluGlyGlyGluAsnSerAsp100105110GlyValPheMetThrGlyGluValProThrAsnGlnIleLeuProAla115120125LeuGluTrpMetThrGluIleGlyValArgLysTrpTyrValIleGly130135140SerAspTyrValTrpProArgLysThrValSerValIleArgGluPhe145150155160LeuAlaSerAsnGlnLeuProSerArgGlyArgSerAspValArgLeu165170175AlaSerCysGluPheLeuSerLeuGlyThrSerAspPheThrSerThr180185190LeuGluAlaIleGluMetSerGlyAlaAspGlyValLeuValLeuLeu195200205LeuGlyGlnAspAlaValGlnPheAsnArgSerPheSerArgLysGly210215220LeuHisArgAspIleValArgLeuSerProLeuMetAspGluAsnMet225230235240LeuLeuAlaSerGlyAlaHisAlaAlaHisGlyLeuTyrSerValSer245250255GlyPhePheGluCysLeuValThrGlyHisSerMetAspPheGluSer260265270ArgTyrIleLysHisPheGlyProThrAlaProProIleThrSerPro275280285GlyGluSerCysTyrGluGlyIleArgLeuLeuAlaThrLeuAlaAsp290295300ArgAlaGlyAspLeuAspProMetSerLeuSerTyrHisAlaAspArg305310315320ThrLeuAspTyrAspSerProArgGlyHisValArgPheAspGlyArg325330335HisLeuAlaGlnAspMetTyrIleAlaArgAlaAspGlyValGluPhe340345350AspValLeuAlaGlnValSerHisVal355360(2) INFORMATION FOR SEQ ID NO:2:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 1086 base pairs(B) TYPE: nucleic acid(C) STRANDEDNESS: double(D) TOPOLOGY: linear(ii) MOLECULE TYPE: protein(iii) ORIGINAL SOURCE:(A) ORGANISM: Rhodococcus rhodochrous(B) STRAIN: J-1(xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:GTGCCCCTCCGCCGACTGAACCTGGGCTTGGTGCTACCTCAGAGT45GGACCGTCCGGCATTTTCGGTCCGTCATGCCAGGCGAGCGCCGAG90TACGCCATCGATGAGCTCAACGCGGGCGGCGGAATCCTGGGCCGA135GAGGTTACGGCGGTCTTCGTTGACGGGGGCGCGGACCCGTCCGCC180GTAGCAGCATGCATCGCCGACCAGACGAAACGTCGGGAATTGGAC225GCCGTAGTCGGGTGGCACACGTCTGCTGTTCGTCGACGCATCGTG270AGCGCCATCGGCGGACGTATTCCGTATGTCTACACCGCAGTCTAC315GAGGGCGGCGAGAACTCCGACGGCGTGTTCATGACGGGAGAGGTA360CCGACGAATCAGATTCTTCCTGCCCTGGAATGGATGACTGAGATC405GGCGTGCGTAAGTGGTATGTCATTGGCAGTGACTACGTTTGGCCT450CGAAAGACTGTCTCGGTCATTCGCGAATTCCTGGCGTCGAACCAG495CTACCGAGTCGAGGCCGCAGCGACGTTCGACTGGCGTCGTGCGAG540TTCTTGTCACTAGGCACATCCGACTTCACTTCAACGCTCGAAGCA585ATTGAGATGTCGGGGGCCGATGGCGTTCTCGTCCTCCTCCTCGGC630CAGGACGCAGTACAGTTCAACCGGTCTTTTTCACGGAAAGGGCTG675CACCGCGACATCGTCAGACTCAGTCCGCTGATGGACGAGAACATG720CTGTTGGCAAGCGGCGCACACGCCGCGCACGGACTCTACTCGGTG765TCGGGGTTCTTCGAGTGCCTGGTCACCGGGCACAGCATGGATTTC810GAATCCAGGTACATCAAGCACTTCGGTCCGACCGCCCCGCCGATC855ACTTCGCCTGGAGAGTCGTGCTACGAGGGCATTCGGCTGTTGGCC900ACTCTTGCAGACCGGGCCGGCGATCTCGACCCGATGTCTCTGAGC945TATCACGCAGACCGTACCCTCGACTACGACAGCCCTCGAGGCCAT990GTCCGCTTCGATGGTCGCCATCTCGCTCAGGACATGTACATCGCG1035CGGGCTGACGGAGTAGAGTTCGACGTCTTAGCGCAGGTTTCCCAT1080GTGTGA1086__________________________________________________________________________

Regulatory gene for the expression of nitrile hydratase gene

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