Nucleotide sequences encoding the expression of a Hantaan virus nucleocapsid protein and G1 and G2 glycoproteins

BACKGROUND OF THE INVENTION
The present invention relates to nucleotide sequences that can be used to produce polypeptides that exhibit the characteristics of the nucleocapsid N protein, or one of two glycoproteins G1 and G2, synthesized by the Hantaan virus. The present invention further relates to a method of producing a Hantaan virus vaccine comprised of at least one of the N protein, G.sub.1 and G2.
Each year, hundreds and thousands of people in endemic areas, such as China and Korea, developed infection by Hantaan virus, the etiological agent of Korean hemorrhagic fever, resulting in high morbidity and mortality, not only among the natives in those areas, but also among visitors and service personnel assigned to those areas. In recent years, Hantaviruses have been isolated from rodent populations in endemic and epidemic areas, as well as here in the United States. There is no known cure for such a viral infection, it being generally allowed to run its course until terminated by death or development of natural immunity against the virus.
Because of the extremely infectious nature of the Hantaan virus, containment of this virus for purposes of study poses a special problem. For this reason, it has not been practicable to grow large quantities of live Hantaan virus in the laboratories to extract its immunogenic portions for vaccination purposes. By the same token, detailed information concerning the Hantaan virus has been limited heretofore. Although some information is available about its RNA genome, for example, there is insufficient information available to permit production of viral antigens in the laboratory without propagating the live Hantaan virus. If the nucleotide sequences encoding antigenic portions of the Hantaan virus can be identified, it would be possible to synthesize such antigens in a cell-free system or to genetically-engineer a vaccine. Furthermore, if Hantaan viral infection can be diagnosed at an early stage, for example, by using viral cDNA probes, proper patient management at such a stage may improve prognosis of the disease.
The Hantaan virus belongs to the Hantavirus genus of the Bunyaviridae family. Viruses in this family all possess tripartite, single-stranded, negative-sense RNA species, designated large (L) , medium (M) and small (S), respectively, in accordance with their respective molecular weights. Each RNA species is enclosed in its own nucleocapsid structure, but all three RNA species are surrounded by a lipid envelope containing two virus-specific glycoproteins, known as G1 and G2 glycoproteins [see Schmaljohn et al, J. Infect. Dis. 148: 1005-1101 (1983) Schmaljohn and Dalrymple, in SEGMENTED NEGATIVE STRAND VIRUSES, R. W. Compans and D. H. Bishop, eds., pp. 117-124 (Academic Press, 1984). The Hantaan virus is negative-sense in that it has to produce a positive-sense, complementary RNA ("cRNA") to act as messenger RNA ("mRNA").
Immunogenic Hantaan viral proteins have been identified by Elliott et al, J. Gen. Virol. 65: 1282-1293 (1984), who showed that sera from patients who had recovered from Hantaan virus infection precipitates three Hantaan viral proteins, a nucleocapsid N protein and G1 and G2 glycoproteins. It was not known, however, which of the three RNA species of Hantaan virus, or which segment(s) of such species, encode for each of the N, G1 and G2 proteins.
In the production of immunogenic proteins for vaccination purposes, it is not desirable to include in such vaccines other proteins or substances of unknown effect which may be harmful, e.g., pyrogenic substances. Therefore, to produce immunogenic proteins using genetic engineering techniques, i.e., in vitro techniques to produce DNA molecules containing novel combinations of genes or nucleotide sequences, it is necessary to know precisely which segment of a genome encodes the desired protein. The uncertainty with regard to which segments of the Hantaan viral genome encode the desired proteins can be more fully appreciated by considering what is known about viruses of the Bunyavirus and Phlebovirus genera, other members of the Bunyaviridae family. The Bunyaviruses S-RNA molecules utilize an overlapping reading frame strategy in its cRNA to encode a nucleocapsid N protein and a non-structural ("NS.sub.S ") protein. See Fuller et al, J. Gen. Virol. 64: 1705-1714 (1983). In other words, if the nucleotide sequence for the CRNA of S-RNA species is represented by the formula 1-2-3-4-5-6-7-8-9-10, the nucleotide sequence encoding the N protein may be represented by the sequence 1-2-3-4-5-6, while the sequence encoding for the NSS protein may be represented by 3-4-5-6-7-8. Therefore, to produce only the N protein of Bunyavirus by genetic engineering techniques, the sequence 1-2-3-4-5-6, but not 7-8, will have to be present.
On the other hand, viruses of the Phlebovirus genus utilize an ambisense coding strategy in their S-RNA: a N protein is encoded by a nucleotide sequence at the 5' end of the cRNA molecule, and a NS.sub.S protein is encoded by a nucleotide sequence at the 5' end of the viral RNA molecule. Synthesis of the N protein by genetic engineering techniques in this instance will require the presence of a nucleotide sequence comprising the 3' end of the viral RNA molecule, while synthesis of the NS.sub.S protein would require the presence of the 5' and of the viral RNA molecule.
In contrast, studies to date on viruses of the Phlebovirus and Bunyavirus genera revealed that a single long open-reading-frame (ORF) coding strategy was employed in their CRNA complementary to M-RNA to encode single gene products comprising both G1 and G2 glycoproteins. In the Bunyaviruses, the M-RNA additionally encodes for a NS.sub.M ("non-structural.sub.M ") polypeptide. In the Phleboviruses, sufficient coding information was found which could produce a NS.sub.M polypeptide, but such polypeptide has not been identified in infected cells. To obtain G1 and G2 glycoproteins but not the NS.sub.M proteins, therefore, the specific nucleotide sequence encoding G1 and G2 glycoproteins will have to be identified so that the sequence encoding for NS.sub.M protein can be excluded.
Based upon the present state of the art, it has been impossible to predict a Priori what coding strategy is utilized in the Hantaan virus, and which segments of its genome comprise the nucleotide sequences that encode the polypeptides corresponding to the immunogenic N protein, and G1 and G2 glycoproteins. In order to produce such proteins without the use of live viruses, however, this information is needed to avoid the production of undesirable proteins.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to identify the nucleotide sequences that can be expressed to obtain polypeptides exhibiting the characteristics of a Hantaan virus nucleocapsid (N) protein or of a G1 or G2 glycoprotein.
It is a another object of the present invention to provide a method of producing immunogenic proteins of Hantaan virus, without the need to propagate live Hantaan viruses.
In accomplishing these and other objects, there has been provided in accordance with one aspect of the present invention, a vector comprising at least one nucleotide sequence selected from the group consisting of a sequence coding for a first polypeptide exhibiting the characteristics of a Hantaan virus nucleocapsid protein and a sequence coding for a second polypeptide that is a precursor of a Hantaan virus glycoprotein. In one preferred embodiment, a vector comprises a nucleotide sequence as described above and a DNA plasmid, pGem 1, which is comprised of a promoter sequence for SP6 polymerase.
In accordance with another aspect of the present invention, there has been provided a cDNA molecule comprising at least one of the abovementioned nucleotide sequences.
In accordance with yet another aspect of the present invention, there has been provided a method of producing a Hantaan virus WWA molecule comprising the step of transcribing a cDNA molecule described above.
In accordance with still another aspect of the present invention, a method of producing a vaccine comprises the steps of translating a Hantaan virus mRNA molecule, as described above, and of purifying a resultant translation product, has been provided.
Further objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial restriction map corresponding, from left to right, to Hantaan virus complementary RNA 5'-3'. The numbers represent nucleotide positions.times.100.
FIG. 2 (which is composed of FIGS. 2A, and 2B) is Hantaian virus S-RNA nuclitidesequences presented as the viral complementary DNA strand, 5'-3'. Nucleotides are numbered on the left end of each line and predicted amino acids for the major open-reading-frame are positioned above their codons.
FIG. 3 (which is composed of FIGS. 3A, 3B, 3C and 3D) is shown on two pages and represents Hantaan virus M-RNA nucleotide sequences presented as the viral complementary DNA strand, 5'-3'. Nucleotide are numbered on the left end of each line and predicted amino acids for the major open-reading-frame are positioned above their codons. Anino terminal of each of G1 and G2 is indicated by a bracket and an arrow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has been discovered that the Hantaan virus utilizes a single long open-reading-frame (ORF) coding strategy, in both its CRNA complementary to S-RNA and cRNA complementary to M-RNA, to encode a single polypeptide which exhibits the characteristics of its nucleocapsid protein and a single polypeptide that is a precursor of the G1 and G2 glycoproteins, respectively. The term "precursor" is used here to denote a polypeptide that is cleaved and glycosylated before it has the characteristics of G1 and C2 glycoproteins. In contrast to other members of the Bunyaviridae family, Hantaan virus S-RNA does not encode a NS.sub.S protein, and its M-RNA does not encode a NS.sub.M protein.
Based upon the discovery of Hantaan virus' coding strategy, cDNA molecules comprising nucleotide sequences that encode viral nucleocapsid protein and glycoproteins can now be constructed and inserted into vectors. A vector in the context of the present invention comprises a first DNA molecule comprising at least one restriction site, e.g., plasmid pGem 1, and a second DNA molecule which can be inserted into said restriction site, e.g., Hantaan virus cDNA, wherein the vector is capable of infecting or transforming a host cell, and of autonomous replication in a host cell or. of employment of a host's enzyme systems for its replication. A restriction site within the present invention comprises a specific nucleotide sequence recognizable by a type II restriction endonuclease and within which it makes a cut in the DNA. Vectors suitable for use in the present invention are described by Maniatis et al, in MOLECULAR CLONING: A LABORATORY MANUAL, Cold Spring Harbor Laboratory, N.Y. (1982), and includes, for example, plasmids pGem 1 and pBR322, and bacteriophage M13.
A cDNA molecule according to the present invention can be made in accordance with generally known laboratory procedures using enzyme reverse transcriptase, Hantaan viral RNA genome as template and a synthetic oligonucleotide as primer. The synthetic oligonucleotide is complementary to the first 17-19 bases at the 3' end of the viral RNA, and is made by the use of a DNA synthesizer, Model 381A, Applied BioSystems, Inc. (San Francisco, CA) in accordance with the manufacturer's directions according to the phosphoramidite method of oligonucleotide synthesis, and based upon the terminal sequence information previously obtained, see Schmaljohn and Dalrymple (1983). Hantaan virus RNA can be extracted in the manner described in detail below. After incubation, the reaction is terminated and the RNA template is degraded. The resultant single-stranded cDNA can be converted into a double-stranded DNA, for example, by the use of DNA polymerase as in the method of Maniatis et al, loc. cit.
A cDNA molecule within the present invention can further comprise at least one of a leader sequence and a tail sequence that are, respectively, a nucleotide sequence that precedes and a nucleotide sequence that follows the sequences for encoding N protein or the precursor of the G1 and G2 glycoproteins. The leader and tail sequences may provide necessary sites upon which enzymes such as endonuclease can act, or may function as a buffer such that, in inserting or removing a desired sequence, the desired sequence itself is not cleaved. In general, the length and the specific nucleotide sequence of leader and/or tail sequence is not crucial so long as the above-mentioned functions are not impaired. In the case of the precursor for G1 and G2 glycoproteins, however, a leader sequence that encodes hydrophobic proteins may be necessary for proper processing of the glycoproteins when they are synthesized in rabbit reticulocyte lysate systems, as described in detail below.
Vectors comprised of Hantaan virus cDNA within the present invention, can be made by inserting double-stranded cDNA of Hantaan virus into replicative forms of plasmids of bacterial origin or into DNA of bacteriophages. Insertion of cDNA can be accomplished, for example, by dC-tailing the cDNA from Hantaan virus and dg-tailing the DNA of the plasmid, and circularizing the recombined plasmid by annealing the "sticky ends" created in this manner, e.g., with the use of ligase.
Examples of a vector comprising a cDNA molecule that encodes a Hantaan virus nucleocapsid N protein, and of a vector comprising a cDNA molecule that encodes a polypeptide that is a precursor of G1 and G2 glycoproteins, are deposited with the American Type Culture Collection (ATCC), 12301 Parklawn Drive, Rockville, Maryland 20852, U.S.A., under accession Nos. 67675 and 67676, respectively.
Vectors made in this way can be used to transform a host cell, for example, Escherichia coli, K-12, strain HB101, which can produce one or more copies of such vectors during each replicative cycle. A host cell can be rendered susceptible to transformation by plasmid, for example, by treatment with calcium chloride. Transformed host cells are then plated on a medium selective for the plasmid, e.g., on a medium comprising tetracycline to select for a tetracycline-resistance determinant carried by plasmid pBR322. Identification of bacterial colonies comprising the Hantaan virus DNA is performed by first transferring the resultant bacterial colonies to multiple plates and replicate filters (Whatman 541), as described, for example, by Grunstein and Hogness, Proc. Natl. Acad. Sci. USA, 72: 3961-3965 (1975), and then probing such filters either with the same synthetic oligonucleotide as used for priming the first strand cDNA synthesis, but phosphorylated at the 5' ends with .gamma.-ATP.sup.32, or with cDNA probes prepared from gel-purified S-RNA or M-RNA primed with random DNA primers.
The Hantaan virus cDNA molecule can be moved from one vector to another to suit the purpose. For example, cDNA inserted into plasmid pBR322 can be excised by partial digestion with PstI, purified by agarose gel electrophoresis and subcloned into M13 bacteriophage for sequencing or into the ERI site of the pGem 1 plasmid (Promega Biotec) , which comprises a SP6 promotor, for purpose of synthesizing RNA.
To produce mRNA from cDNA within the present invention, the plasmid comprising Hantaan virus cDNA can be linearized at unique restriction sites adjacent to the cloning site, that is, the site of insertion of cDNA, and RNA can be transcribed using a DNA-dependent RNA polymerase. In particular, plasmid pGem 1 comprising Hantaan viral cDNA can be linearized at unique XbaI or SAlI restriction sites adjacent to the PstI cloning site, and RNA can be synthesized by addition of SP6 polymerase (Promega Biotec), used in accordance with manufacturer's directions. The mRNA molecules produced in this manner can be purified by known laboratory techniques.
mRNA generated in accordance with the present invention can be used to program cell-free rabbit reticulocyte lysate translation systems to generate Hantaan viral proteins. The resultant proteins can be purified by immune-precipitation using antisera prepared against whole virions, by adsorption to a column comprising such antisera, or by polyacrylamide gel electrophoresis, in accordance with known laboratory techniques.
Antisera against Hantaan virus or its immunogenic proteins within the present invention can be obtained from ascitic fluid of mice hyper-immunized with Hantaan virus or its N, G1 or G2 proteins and subsequently injected with Sarcoma 180 cells, in accordance with the method of Brandt et al, Amer. J. Trop. Med. Hyg. 16: 339-347 (1967). In particular, adult female ICR mice are injected both subcutaneously and intramuscularly on days 0, 3 and 28 with a suspension of suckling mouse brains of sick and moribund mice previously inoculated with Hantaan virus strain ATCC VR-938. Sarcoma 180 cells are then injected and ascitic fluid is collected ten to fourteen days after final inoculation of Hantaan virus. From the hyperimmunized mice can be drawn ascitic fluid comprising antibodies against Hantaan virus or its proteins, which fluid is pooled and clarified by centrifugation. Antibody titer in the ascitic fluid can be assayed by plaque-reduction neutralization, hemagglutination inhibition, and radioimmune assay.
The present invention is further described below by reference to the following example.
EXAMPLE 1
Analysis and characterization of a Hantaan virus nucleotide sequence which encodes a polypeptide exhibiting the characteristics of a nucleocapsid N protein.
It was found that Hantaan virus utilized a single long ORF coding strategy in its cRNA complementary to viral S-RNA to encode a single polypeptide that exhibited the characteristics of Hantaan virus nucleocapsid N protein. The reading frame for this polypeptide was found to begin at the 37th nucleotide from the 5' end and to terminate at the 370th nucleotide from the 3' end, see Schmaljohn et al, Virol. 155: 633-643 (1986), the contents of which are hereby incorporated by reference.
A cDNA molecule in accordance with the present invention, when inserted into a plasmid, e.g., pGem 1, was found to be capable of encoding RNA which could be translated to produce polypeptides indistinguishable from Hantaan virus N protein by polyacrylamide gel electrophoresis and by specific immune-precipitation using polyclonal, anti-Hantaan sera or monoclonal antibodies directed against Hantaan virus N protein. These polypeptides have a molecular weight of about 48,100, consistent with its predicted molecular weight of about 50, 000 daltons. The polypeptide predicted on the basis of the nucleotide sequence was approximately 429 amino acids long.
A. Propagation of Hantaan Virus In Vitro
Hantaan virus, strain ATCC VR-938, was propagated in Vero E6 cells (ATCC No. C1008), purified, and its total RNA extracted in accordance with the procedure in Schmaljohn et al (1983). Essentially, the virus was propagated in E6 cells, at multiplicities of infection of less than 0.1, in 30 ml of growth medium comprised of Eagle's minimal essential medium containing Earles' salts, 10% heated fetal bovine serum, 100 units of penicillin, 100 .mu.g/ml of streptomycin, 0.5 .mu.g/ml of Fungizone.RTM., (Gibco, Grand Island, NY) and 60 .mu.g/ml of Tylocine.RTM. (Gibco), in 150-cm.sup.2 plastic tissue culture flasks and incubated at 37'C. viruses from a second Vero E6 passage were used for isolation of RNA. Growth medium was removed 4 days post-infection and replaced with fresh growth medium. Infected cell culture supernatants were harvested 8 days post-infection, and clarified by centrifugation for 30 minutes at 7,900 g at 4'C in a Sorvall GSA rotor (Dupont, Newtown, CT). The virus in the supernatant was concentrated by polyethylene glycol precipitation by adding solid polyethylene glycol 6,000 (Sigma Chemical Co., St. Louis, MO) to a final concentration of 8% and sodium chloride to a final concentration of 0.5M, stirring the mixture for 4 hours at 4'C, and collecting the precipitated virus by centrifugation at 7,900 g, for 30 minutes in a Sorvall GSA rotor. Pellets were resuspended in a mixture of 0.01M Tris, 0.1M NaC1 and 0.001M EDTA (hereafter referred to as "TNE"), pH 7.4, then layered on a 10%-60% sucrose-TNE gradient and centrifuged for 2-24 hours in a model SW-41 (Beckman Instruments, Cedar Crove, NJ) at 195,000 g. Fractions from the sucrose gradient were collected, and virus-containing fractions were identified by scintillation counting of radiolabeled virus, or solid-phase radioimmune assay ("RIA") , as described below.
For radiolabeling of Hantaan virus, infected E6 cell cultures were radiolabeled from four to eight days after infection with one of (.sup.35 S]methionine at 10 .mu.Ci/ml, .sup.3 H-labeled mixed amino acids, at 10 .mu.Ci/ml, [.sup.3 H]uridine at 30 .mu.Ci/ml, or (.sup.32 P)orthophosphate at 150 .mu.Ci/ml.
For solid-phase RIA, known laboratory methods can be employed, for example, as described by Schmaljohn et al, (1983). In particular Hantaan virus antiserum used for antigen detection was a 1 in 50 dilution of recalcified plasma from a convalescent patient who acquired clinical Korean Hemorrhagic fever while living in Korea. Protein A (Pharmacia, Piscataway, NJ) iodinated with .sup.125 I (Amersham, Arlington Heights, IL) by chloramine T method was used to detect human IgG. Viral titer was assayed by plaque formation on Vero E6 monolayers with the use of an overlay consisting of 0.6% agarose in the growth medium. The monolayers were incubated for eight to ten days prior to neutral red staining.
B. Extraction of Hantaan Virus RNA
To extract Hantaan virus RNA, viruses prepared above were placed in TNE containing 1% SDS, and an equal volume of a saturated solution of TNE in a solution comprising 500 ml of phenol, 70 ml of cresol, and 0.5 g of 8-hydroxy-quinoline was added to the viruses. Total viral RNA was recovered in the aqueous phase following centrifugation at 13,400 g in a Sorvall HB-4 rotor (Difco) for 10 minutes, reextracted with the above-mentioned phenol solution, and precipitated with cold ethanol and 0.3M sodium acetate. RNA extracted in this manner was used either directly as template for cDNA synthesis or was separated into L-, M- and S-RNA species prior to such use. Separation of RNA species was accomplished by dissolving RNA in 10 mM sodium phosphate, pH 7.0, and subjecting the solution to horizontal agarose gel electrophoresis on a subcell electrophoresis unit (Bio-Rad Laboratories, Richmond, CA) for 8 to 12 hours at 40 V. The agarose gels consisted of 1.4% SeaPlaque.RTM. agarose (Marine Colloids, Rockland,, ME), 10 mM sodium phosphate, pH 7.0.
C. Generation of cDNA
First-strand cDNA was synthesized in a DNA synthesizer, as described above, using the viral RNA extracted above as a template and, as a primer, a synthetic oligonucleotide, 5'-TAGTAGTAGACTCCCTA-3', complementary to 17 bases at the 3' end of Hantaan virus S-RNA, as described above. In particular, approximately 50 .mu.g of total virion RNA in water and 1 .mu.g of primer were incubated at room temperature for 10 minutes in the presence of methylmercury hydroxide, at 10 mM final concentration (Alfa Biochemicals, Denvers, MA) . The RNA/primer mixture in approximately 5.5 .mu.l was then treated with 1 .mu.l of 700 mM 2-mercaptoethanol (Sigma) and added to a reaction mixture containing:
(a) 3 .mu.l of 2.5 mM of each of dATP, dCTP, dGTP and DTTP (Pharmacia, Piscataway, N.J.),
(b) 3 .mu.l of a 5X buffer comprising 250 mM Tris-HC1, pH 8.3, 50 Mm 50 MgCl.sub.2, 50 mM dithiothreitol, 350 Mm KCl,
(c) 1 .mu.l of RNAsin (Promega Biotec, Madison, WI), and
(d) 1.5 .mu.l of AMV reverse transcriptase (15 units/.mu.l, Life Sciences, Inc., St. Petersburg, FL).
The combined mixture was incubated for 2 hours at 42'C, and the reaction terminated by addition of 2 .mu.l of 0.5M EDTA, pH 8.0. The RNA template was then degraded by incubating the cDNA/RNA complex in 150 Mm N2OH at 65'C for 1 hour. Single stranded cDNA was recovered by ethanol precipitation.
D. Production of Vectors
Single-stranded DNA prepared as described above was converted to double-stranded DNA with the large fragment of DNA polymerase I (Pharmacia) in accordance with known laboratory procedures. After S1 nuclease treatment and dC tailing, cDNA was annealed to PstI-cleaved, dG-tailed pBR322 (New England Nuclear, Boston, MA) . The annealed plasmid was used to transform Escherichia coli K-12, strain HB101, which was then plated on Luria-Bertani agar plates containing 20 .mu./ml of tetracycline. Resultant bacterial colonies were transferred to multiple plates and replicate filters (Whatman 541). Bacterial colonies which contained Hantaan virus cDNA were identified by probing the filters either with the same synthetic oligonucleotide as used for priming first-strand cDNA synthesis, except for being phosphorylated at the 5' ends with .gamma.-ATP.sup.32, or with radiolabeled cDNA probes prepared from gel-purified S-RNA and random DNA primers.
E. Identification of Nucleotide Sequence.
Nucleotide sequence of Hantaan virus cDNA were identified as described above. Three clones of cDNA, S8, S16 and S86 which appeared of sufficient length to encompass most or all of Hantaan virus S-RNA were selected for restriction mapping. and sequence analysis. The sequence S8 was determined both by chemical cleavage method of Maxam and Gilbert (1980), and by the dideoxy chain termination method of Sanger et al (1977). S16 and portions of S86 were sequenced by the dideoxy method with M13 specific primers. Nucleotide sequence determined by these methods can be analyzed manually or with the aid of a computer using known programs, for example, Intelligenetics sequence-analysis program or University of Minnesota sequence-analysis program, to generate information regarding, e.g., composite sequence of S-RNA and M-RNA, restriction enzyme cleavage sites, and glycosylation sites. A partial restriction map of Hantaan virus S-RNA is shown in FIG. 1. A consensus nucleotide sequence of S8, S16 and S86 is shown in FIG. 2.
Clone S86 was found to have complementary sequences in its 5' and 3' terminals which included 20 of the terminal 22 nucleotides. Since viruses of the Bunyaviridae family generally have terminal nucleotide complementarity, S86 is believed to comprise a complete copy of the S segment of Hantaan virus.
F. Generation of mRNA from cDNA.
For generation of mRNA, the genetically-engineered vector described above, comprising pGem 1 plasmid and Hantaan virus cDNA, was used to transform a bacterial host, E. coli, K-12, strain HB101, and the transformed host was propagated to generate multiple copies of such vectors. Vectors were separated from host DNA after lysis of cells, for example, by lysozyme treatment or treatment on ice in a lysis buffer containing 10 mM Tris-HC1, pH 8.0, 1 mM EDTA, 0.5M NaCl, 0.25 mg/ml each of aprotinin and .alpha..sub.2 -macroglobulin (Sigma) and 4% Zwittergent 3-14 (Calbiochem-Behring, San Diego, CA). Cell nuclei and cellular debris were removed by centrifugation at 13,000 g for 5 minutes at 4'C. The supernatant was then subjected to agarose gel electrophoresis. The vectors thus obtained were linearized at unique XbaI or SAII restriction sites adjacent to the PstI cloning site. SP6 was added to the linearized vectors for transciption of RNA from DNA, in accordance with manufacturer's directions (Promega Biotec). The cDNA templates were then digested.
G. Cell-Free Translation of RNA
RNA generated from Hantaan virus cDNA as described above was used to program a cell-free translation system. Although a rabbit reticulocyte lysate was used for this purpose, any cell-free system is suitable if it is capable of supporting the cleavage and glycosylation of the precursor polypeptide, thereby to generate G1 and G2. Such suitable lysate systems are commercially available (e.g., from New England Nuclear, Promega Biotec, Amersham, and Bethesda Research Laboratories, among others) and can be used in accordance with manufacturer's directions. Resultant polypeptides can be purified by generally known laboratory methods.
No demonstrable products were translated from RNA in the virion orientation, but numerous translation products could be identified when lysates were programmed with RNA transcripts in the Hantaan virus CRNA orientation. The largest and most abundant translation product was found by polyacrylamide gel electrophoresis, as described below, to be indistinguishable from N protein isolated from Hantaan virus. This polypeptide could be immune-precipitated using the above-described polyclonal, anti-Hantaan sera or monoclonal antibodies directed against Hantaan N protein. A variety of smaller products, presumably formed from premature termination of translation, were occasionally precipitated from translation mixtures. No polypeptides other than Hantaan virus N protein, however, were specifically and consistently immune-precipitated.
H. Polyacrylamide Gel Electrophoresis ("PAGE") of Viral Proteins
Viral proteins were obtained from lysis of Vero E6 cells about eight days after infection of such cells with Hantaan virus. Cells were lysed on ice in a lysis buffer and cell nuclei and cellular debris were removed as described above. Virus-specific proteins were immune precipitated from infected cell lysates by incubation with antisera on ice overnight followed by the addition of 100 .mu.l of 50% protein A-Sepharose (Sigma) and continued incubation for 30 minutes. Precipitates were washed three times in 1 in 2 dilution of the lysis buffer described above, and once in 10 Mm Tris-HCl, pH 6.7. Electrophoresis was performed at 100 V for 12 hours in SDS-containing polyacrylamide gels, for example, as disclosed by Laemmli, Nature 227: 680-685 (1970). In particular, viral proteins were dissociated by addition of an equal volume of 0. 5M Tris-HCl , pH 6.7, containing 5% SDS and 4% -mercaptoethanol. These samples were boiled for 2 minutes prior to electrophoresis. Electrophoresis was conducted in discontinuous gels comprising acrylamide:N,N'diallyltartardiamide (DATD), at a ratio of 30:1.41, at 100 V for about 5 hours in a 0.025M Tris and 0.2M glycine buffer, at pH 8.3. The resolving gel consisted of 12% acrylamide:DATD, 0.1% SDS, and 0.375M Tris-HCl , pH 8.9. The stacking gel consisted of 3.6% acrylamide:DATD, 0.1% SDS, and 0.062M Tris-HCl , pH 6.7.
EXAMPLE 2
Analysis and characterization of a Hantaan virus nucleotide sequence which encodes a polypeptide that is a precursor of G1 and G2 glycoproteins
It was found that Hantaan virus utilized a single long ORF coding strategy in its CRNA complementary to viral M-RNA to encode a single polypeptide that is a precursor of Hantaan virus glycoproteins G1 and G2. It was further found that protein synthesis began at nucleotide positions 41-43 and terminated at nucleotide positions 3446-3448, encoding a total of 1135 amino acids, see Schmaljohn et al, Virol. 157: 31-39 (1987), the contents of which are hereby incorporated by reference. It was also found that this polypeptide comprised a precursor of both G1 and G2 glycoproteins, the gene sequence being 5'-G1-G2-3'. It is not known, however, how this polypeptide is cleaved to generate G1 and G2 glycoproteins. The amino acid sequence of G1 was found to extend at least from amino acid 19 to include amino acids 588-614 while the amino acid sequence of G2 was found to extend from amino acid 649 to include amino acids 1127-1135. Seven putative glycosylation sites, predicted on the basis of amino acid sequence Asn-X-ser/Thr, where X represents any amino acid, are indicated by parentheses and an * in FIG. 3. G1 was found to have a molecular weight of about 64,000 daltons, while G2 was found to have a molecular weight of about 54,000 daltons, close to its predicted values of 62 K and 52 K, respectively.
A. Generation and Sequence Analysis cDNA
Hantaan virus was propagated in Vero E6 cells and virion RNA extracted as in Example 1 above. First strand cDNA synthesis was accomplished as in Example 1 except the synthetic oligonucleotide used was 5'-TAGTAGTAGACTCCGCAAA-3', complementary to nineteen bases at the 3' end of virion M-RNA. Double-stranded cDNA was synthesized, tailed, and inserted into the PstI site of pBR322, and recombinant plasmids were identified as in Example 1, except that the transformed bacterial colonies were probed with radiolabeled cDNA prepared from gel-purified M-RNA. Sequence analysis of the cDNA molecules was performed by the dideoxy chain termination method of Sanger et al (1977), using cDNA subcloned into bacteriophage M13 as templates and synthetic oligonucleotides complementary to portions of M13 and/or such cDNA as primers. Sequence data were analyzed as described above.
Comparison of the 5' and 3' terminals of a large cDNA clone complementary to virion M-RNA showed complementary sequences for eighteen bases including all but the three most distal nucleotides complementary to the virion RNA sequence. Since 3' and 5' complementarity is a general feature of Bunyaviridae family, this clone was believed to represent the entire M-RNA segment except for six bases corresponding to the 3' terminus and three bases corresponding to the 5' terminus of virion RNA. A base composition for the entire virion M-RNA was determined from cDNA sequence information to be 29.9% A, 17.9% G, 21.4% C, and 30.8% U.
A single long ORF was detected in the nucleotide sequence complementary to viral CRNA. The nucleotide sequence of a large clone of cDNA complementary to viral M-RNA was identified, as shown in FIG. 3.
B. Gneeration of RNA and G1 and G2 Glycoproteins
Hantaan viral mRNA was generated from cDNA complementary to M-RNA in the same manner as described in Example 1. This mRNA was also similarly translated in rabbit reticulocyte lysate translation systems. The resulting proteins were purified by precipitation with antisera or by polyacrylamide gel electrophoresis, in accordance with known laboratory procedures. A total of 1135 amino acids were encoded from the first ATG until a termination codon, TAG, occurred at nucleotide position 3446-3448. Gene order, determined by partial amino acid analysis of the amino-terminal of G1 and G2, as described below, was found to be 5'-G1-G2-3'.
C. Amino-terminal Sequence Analysis of G1 and G2
To determine the gene order of the Hantaan virus M-RNA and to locate the amino terminals of G1 and G2, viral G1 and G2 glycoproteins were isolated and subjected to amino-terminal sequence analysis. These glycoproteins were prepared for amino-terminal sequence analysis by electrophoresis through polyacrylamide gels in accordance with known laboratory techniques. In particular, proteins were boiled in 65 mM Tris-borate, pH 8.4, containing 1% SDS, 5% 2-mercaptoethanol, and 10% glycerol and applied to a 3 mm-thick, discontinuous, polyacrylamide gel. A 60-ml separating gel of 10% acrylamide and 0.05% bisacrylamide was prepared in 0.17M Tris-sulfate, pH 8.4. Gels were allowed to polymerize for at least 24 hours and were electrophoresed at 100 V for approximately 12 hours, after which they were sliced horizontally. Proteins were recovered from gel slices by agitation in 50 Mm ammonium bicarbonate containing 0.1% SDS for two separate 12-hour periods. Samples were lyophilized and dialyzed extensively against water. Approximately 100 pmol of purified proteins was sequenced on Model 470A protein sequencer (Applied Biosystems Inc.) and analyzed with a 120A on-line PTH analyzer. A partial amino acid sequence of (NH.sub.2)-Leu-X-X-Val-Tyr-Asp-Met-Lys-Ile-Glu-X-Pro-His-Thr -Thr-Val was determined for G1 and (NH.sub.2)-X-Glu-X-Pro -Leu-X-Pro-Val-Trp-Asn-Asp-Asn-Ala-His-Gly-val-Gly for G2, where X represented unidentified amino acids. These sequences were found to correspond to those derived from cDNA beginning at nucleotide positions 95-97 for G1 and 1985-1987 for G2, therefore, establishing the gene order of M-RNA as 5'-G1-G2-3'.
The carboxy terminal of G1 and G2, respectively, was identified by synthesizing peptides, corresponding to amino acids 588-614, i.e., NH.sub.2 -Tyr-Lys-Val-Cys-Gln-Val-Thr-His-Arg-Phe-Arg-Asp -Asp-Leu-Lys-Lys-Thr-Val-Thr-Pro-Gln-Asn-Phe-Thr-Pro-Gly-Cys-COOH, and 1127-1135, i.e., NH.sub.2 -Cys-Pro-Val-Arg-Lys-His-Lys-Lys-Ser-COOH, of the ORF respectively, as described below, injecting such polypeptides into rabbits to generate antisera and testing, by immune precipitation, the ability of the antisera to recognize G1 and G2 extracted from Hantaan virus.
D. Peptide Synthesis and Immune Precipitation
Peptides representing derived amino acid sequences were synthesized with an Applied Biosystems, Inc. Model 430A peptide synthesizer. Peptides were cleaved from the resin with hydrofluoric acid and coupled to keyhole limpet hemocyanin.
Approximately 1-1.5 mg of each coupled peptide was injected intradermally with Freund's complete adjuvant into four shaved sites on each of two young female New Zealand white rabbits. Rabbits were boosted with approximately 1.5 mg of coupled peptides in Freund's incomplete adjuvant at 2-week intervals and bled from 10 to 14 days post-boost. Rabbit sera were preadsorbed with uninfected Vero E6 cells prior to use in Hantaan immune-precipitation experiments. Polyclonal rabbit antisera consisted of convalescent sera collected 4-12 weeks following infection of New Zealand white rabbits with Hantaan virus, strain 76-118.
For immune precipitation, intracellular viral proteins were radiclabeled with [.sup.35 S]methionine, at 100 .mu.Ci per 25-cm.sup.2 flask of confluent Vero E6 cells, from 24 to 48 hours post-infection and isolated as described above.

Nucleotide sequences encoding the expression of a Hantaan virus nucleocapsid protein and G1 and G2 glycoproteins

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Schmaljohn et al. 1986 Virology 155: 633-643.
Schmaljohn et al., 1987 Virology 157: 31-39.
Yoo et al., 1987 NAR 15:6299-6300.