Pseudorabies virus protein

Abstract: The present invention provides recombinant DNA molecules comprising a sequence encoding a pseudorabies virus (PRV) glycoprotein selected from the group consisting of gl, gp50, and gp63, host cells transformed by said recombinant DNA molecule sequences, the gl, gp50 and gp63 polypeptides. The present invention also provides subunit vaccines for PRV, methods for protecting animals against PRV infection and methods for distinguishing between infected and vaccinated animals.

Description: FIELD OF INVENTION This Invention relates to DNA sequences encoding pseudorabies virus glycoproteins and polypeptides related thereto. These DNA sequences are useful for screening animals to determine whether they are infected with PRV and also for expressing the glycoproteins encoded thereby. BACKGROUND OF THE INVENTION Pseudorabies virus (PRV) is a disease which infects many species of animals worldwide. PRV infections are variously called infectious Bulbar paralysis, Aujeszky's disease, and mad itch. Infections are known in important domestic animals such as swine, cattle, dogs, cats, sheep, rats and mink. The host range is very broad and Includes most mammals and, experimentally at least, many kinds of birds (for a detailed list of hosts, see D.P. Gustafson, "Pseudorabies", in Diseases of Swine, 5th ed., A.D. Leman et al., eds., (1981)). For most infected animals the disease is fatal. Adult swine and possibly rats, however, are not killed by the disease and are therefore carriers. Populations of swine are particularly susceptible to PRV. Although the adult swine rarely show symptoms or die from the disease, piglets become acutely ill when infected and death usually ensues in 24 to 48 hours often without specific clinical signs (T.C. Jones and R.D. Hunt, Veterinary Pathology, 5th ed., Lea & Febiger (1983)). PRV vaccines have been produced by a variety of techniques and vaccination in endemic areas of Europe has been practiced for more than 15 years. Losses have been reduced by vaccination, but vaccination has maintained the virus in the environment. No vaccine has been produced that will prevent infection. Vaccinated animals that are exposed to virulent virus survive the infection and then shed more virulent virus. Vaccinated animals may therefore harbor a latent infection that can flare up again. (See, D.P. Gustafson, supra). Live attenuated and inactivated vaccines for PRV are available commercially in the United States and have been approved by the USDA (See, C.E. Aronson, ed., Veterinary Pharmaceuticals & Biologicals, (1983)). Because adult swine are carriers of PRV, many states have instituted screening programs to detect infected animals. DNA/DNA hybridization can be used to diagnose actively infected animals utilizing the DNA sequence of the instant invention. Some of the PRV glycoproteins of the present invention are also useful in producing diagnostics for PRV infections and also to produce vaccines against PRV. PRV is a herpesvirus. The herpesviruses generally are among the most complex of animal viruses. Their genomes encode at least 50 virus specific proteins and contain upwards of 150,000 nucleotides. Among the most immunologically reactive proteins of herpesviruses are the glycoproteins found, among other places, in virion membranes and the membranes of infected cells. The literature on PRV glycoproteins refers to at least four viral glycoproteins (T. Ben-Porat and A.S. Kaplan, Virology, 41, pp. 265-73 (1970); A.S. Kaplan and T. Ben-Porat, Proc. Natl. Acad. Sci. USA, 66, pp. 799-806 (1970)). INFORMATION DISCLOSURE M.W. Wathen and L.K. Wathen, J. Virol., 51, pp. 57-62 (1984) refer to a PRV containing a mutation in a viral glycoprotein (gp50) and a method for selecting the mutant utilizing neutralizing monoclonal antibody directed against gp50. Wathen and Wathen also indicate that a monoclonal antibody directed against gp50 is a strong neutralizer of PRV, with or without the aid of complement, and that polyvalent immune serum is highly reactive against gp50, therefore concluding that gp50 may be one of the important PRV immunogens. On the other hand, it has been reported that monoclonal antibodies that react with the 98,000 MW envelope glycoprotein neutralize PRV infectivity but that monoclonal antibodies directed against some of the other membrane glycoproteins have very little neutralizing activity (H. Hampl, et al., J. Virol., 52, pp. 583-90 (1984); and T. Ben-Porat and A.S. Kaplan, "Molecular Biology of Pseudorabies Virus", in B. Roizman ed., The Herpesviruses, 3, pp. 105-73 (1984)). L.M.K. Wathen, et al., Virus Research, 4, pp. 19-29 (1985) refer to the production and characterization of monoclonal antibodies directed against PRV glycoproteins identified as gp50 and gp83 and their use for passively immunizing mice against PRV infection. A.K. Robbins, et al., "Localization of a Pseudorabies Virus Glycoprotein Gene Using an E. coli Expression Plasmid Library", in Herpesvirus, pp. 551-61 (1984), refer to the construction of a library of E. coli plasmids containing PRV DNA. They also refer to the identification of a PRV gene that encodes glycoproteins of 74,000 and 92,000 MW. They do not refer to the glycoproteins of the instant invention. A.K. Robbins, et al., European patent application No. 85400704.4 (publication No. 0 162 738) refers to the isolation, cloning and expression of PRV glycoproteins identified as gII and gIII. They do not refer to the PRV glycoproteins of the instant invention. T.C. Mettenleiter, et al., "Mapping of the Structural Gene of Pseudorabies Virus Glycoprotein A and Identification of Two Non-Glycosylated Precursor Polypeptides", J. Virol., 53, pp. 52-57 (1985), refer to the mapping of the coding region of glycoprotein gA (which they equate with gI) to the BamHI 7 fragment of PRV DNA. They also state that the BamHI 7 fragment codes for at least three other viral proteins of 65K, 60K, and 40K MW. They do not disclose or suggest the DNA sequence encoding the glycoproteins of the instant invention or the production of such polypeptides by recombinant DNA methods. B. Lomniczi, et al., "Deletions in the Genomes of Pseudorabies Virus Vaccine Strains and Existence of Four Isomers of the Genomes", J. Virol., 49, pp. 970-79 (1984), refer to PRV vaccine strains that have deletions in the unique short sequence between 0.855 and 0.882 map units. This is in the vicinity of the gI gene. T.C. Mettenleiter, et al., "Pseudorabies Virus Avirulent Strains Fail to Express a Major Glycoprotein", J. Virol., 56, pp. 307-11 (1985), demonstrated that three commercial PRV vaccine strains lack glycoprotein gI. We have also found recently that the Bartha vaccine strain contains a deletion for most of the gp63 gene. T.J. Rea et al., J. Virol., 54, pp. 21-29 (1985), refers to the mapping and the sequencing of the gene for the PRV glycoprotein that accumulates in the medium of infected cells (gX). Included among the flanking sequences of the gX gene shown therein is a small portion of the gp50 sequence, specifically beginning at base 1682 of Figure 6 therein. However, this sequence was not identified as the gp50 sequence. Furthermore, there are errors in the sequence published by Rea et al. Bases 1586 and 1603 should be deleted. Bases should be inserted between bases 1708 and 1709, bases 1737 and 1738, bases 1743 and 1744 and bases 1753 and 1754. The consequence of these errors in the published partial sequence for gp50 is a frameshift. Translation of the open reading frame beginning at the AUG start site would give an incorrect amino-acid sequence for the gp50 glycoprotein. EP-A-0133200 refers to a diagnostic antigenic factor to be used together with certain lectin-bound PRV glycoprotein subunit vaccines to distinguish carriers and non-carriers of PRV. SUMMARY OF INVENTION The present invention provides recombinant DNA molecules comprising operatively linked to an expression control sequence, DNA sequences encoding polypeptides displaying PRV glycoprotein gp50, gp63 or gI antigenicity, wherein the expression control sequence is not naturally operatively linked to the DNA sequence encoding a polypeptide displaying pseudorabies virus glycoprotein gp50, gp63 or gI immunogenicity. The glycoprotein and corresponding DNA sequences are set forth in Charts A, B and C. More particularly, the present invention provides host cells transformed with recombinant DNA molecules comprising the DNA sequences. The present invention also provides the use of gp63 and gI polypeptides, for serological distinction between vaccinated and infected animals. DETAILED DESCRIPTION OF INVENTION The existence and location of the gene encoding glycoprotein gp50 of PRV was demonstrated by M.W. Wathen and L.M. Wathen, supra. The glycoprotein encoded by the gene was defined as a glycoprotein that reacted with a particular monoclonal antibody. This glycoprotein did not correspond to any of the previously known PRV glycoproteins. Wathen and Wathen mapped a mutation resistant to the monoclonal antibody, which, based on precedent in herpes simplex virus (e.g., T.G. Holland et al., J. Virol., 52, pp.566-74 (1984)), maps the location of the structural gene for gp50. Wathen and Wathen mapped the gp50 gene to the smaller SalI/BamHI fragment from within the BamHI 7 fragment of PRV. Rea et al, supra, have mapped the PRV glycoprotein gX gene to the same region. The PRY gp63 and gI genes were isolated by screening PRV DNA libraries constructed in the bacteriophage expression vector λgt11 (J.G. Timmins, et al., "A method for Efficient Gene Isolation from Phage λgt11 Libraries: Use of Antisera to Denatured, Acetone-Precipitated Proteins", Gene, 39, pp. 89-93 (1985); R.A. Young and R.W. Davis, Proc. Natl.Acad. Sci. USA, 80, pp. 1194-98 (1983); R.A. Young and R.W. Davis, Science, 222, pp.778-82 (1983)). PRV genomic DNA derived from PRV Rice strain originally obtained from D.P. Gustafson at Purdue University was isolated from the cytoplasm of PRV-infected Vero cells (ATCC CCL 81). The genomic DNA was fragmented by sonication and then cloned into λgt11 to produce a λ/PRV recombinant (λPRV) DNA library. Antisera for screening the λPRV library were produced by inoculating mice with proteins isolated from cells infected with PRV (infected cell proteins or ICP's) that had been segregated according to size on SDS gels, and then isolating the antibodies. The λPRV phages to be screened were plated on a lawn of E. coli. λgt11 contains a unique cloning site in the 3' end of the lacZ gene. Foreign DNA's inserted in this unique site in the proper orientation and reading frame produce, on expression, polypeptides fused to β-galactosidase. A nitrocellulose filter containing an inducer of lacZ transcription to enhance expression of the PRV DNA was laid on top of the lawn. After the fusion polypeptides expressed by λPRV's had sufficient time to bind to the nitrocellulose filters, the filters were removed from the lawns and probed with the mouse antisera. Plaques producing antigen that bound the mice antisera were identified by probing with a labeled antibody for the mouse antisera. Plaques that gave a positive signal were used to transform an E. coli host (Y1090, available from the ATCC, Rockville, MD 20852). The cultures were then incubated overnight to produce the λPRV phage stocks. These phage stocks were used to infect E. coli K95 (D. Friedman, in The Bacteriophage Lambda, pp. 733-38, A.D. Hershey, ed. (1971)). Polypeptides produced by the transformed E. coli K95 were purified by preparative gel electrophoresis. Polypeptides that were overproduced (due to induction of transcription of the lacZ gene), having molecular weights greater than 116,000 daltons, and which were also absent from λgt11 control cultures were β-galactosidase-PRV fusion proteins. Each individual fusion protein was then injected into a different mouse to produce antisera. Labeled PRV ICP's were produced by infecting Vero cells growing in a medium containing, for example, 14 C-glucosamine (T.J. Rea, et al., supra.). The fusion protein antisera from above were used to immunoprecipitate these labeled ICP's. The polypeptides so precipitated were analyzed by gel electrophoresis. One of them was a 110 kd MW glycoprotein (gI) and another a 63 kd MW glycoprotein (gp63). The genes cloned in the phages that produced the hybrid proteins raising anti-gI and anti-gp63 serum were thus shown to be the gI and gp63 genes. These genes were found to map within the BamHI 7 fragment of the PRV genome (T.J. Rea, et al., supra.) as does the gp50 sequence (see Chart D). The gI location is in general agreement with the area where Mettenleiter, et al., supra, had mapped the gI gene. However, Mettenleiter, et al. implied that the gI gene extends into the BamHI 12 fragment which it does not. This λPRV gene isolation method is rapid and efficient when compared to DNA hybridization and to in vitro translation of selected mRNAs. Because purified glycoproteins were unavailable, we could not construct, rapidly, oligonucleotide probes from amino acid sequence data, nor could we raise highly specific polyclonal antisera. Therefore we used the method set forth above. As mentioned above, the genes encoding gp50, gp63, and gI mapped to the BamHI 7 fragment of the PRV DNA. The BamHI 7 fragment from PRV can be derived from plasmid pPRXh1 (also known as pUC1129) and fragments convenient for DNA sequence analysis can be derived by standard subcloning procedures. Plasmid pUC1129 is available from E. coli HB101, NRRL B-15772. This culture is available from the permanent collection of the Northern Regional Research Center Fermentation Laboratory (NRRL), U.S. Department of Agriculture, in Peoria, Illinois, U.S.A. E. coli HB101 containing pUC1129 can be grown up in L-broth by well known procedures. Typically the culture is grown to an optical density of 0.6 after which chloramphenicol is added and the culture is left to shake overnight. The culture is then lysed by, e.g., using high salt SDS and the supernatant is subjected to a cesium chloride/ ethidium bromide equilibrium density gradient centrifugation to yield the plasmids. The availability of these gene sequences permits direct manipulation of the genes and gene sequences which allows modifications of the regulation of expression and/or the structure of the protein encoded by the gene or a fragment thereof. Knowledge of these gene sequences also allows one to clone the corresponding gene, or fragment thereof, from any strain of PRV using the known sequence as a hybridization probe, and to express the entire protein or fragment thereof by recombinant techniques generally known in the art. Knowledge of these gene sequences enabled us to deduce the amino acid sequence of the corresponding polypeptides (Charts A-C). As a result, fragments of these polypeptides having PRV immunogenicity can be produced by standard methods of protein synthesis or recombinant DNA techniques. As used herein, immunogenicity and antigenicity are used interchangeably to refer to the ability to stimulate any type of adaptive immune response, i.e., antigen and antigenicity are not limited in meaning to substances that stimulate the production of antibodies. The primary structures (sequences) of the genes coding for gp50, gp63, and gI also are set forth in Charts A-C. The genes or fragments thereof can be extracted from pUC1129 by digesting the plasmid DNA from a culture of NRRL B-15772 with appropriate endonuclease restriction enzymes. For example, the BamHI 7 fragment may be isolated by digestion of a preparation of pUC1129 with BamHI, and isolation by gel electrophoresis. All restriction endonucleases referred to herein are commercially available and their use is well known in the art. Directions for use generally are provided by commercial suppliers of the restriction enzymes. The excised gene or fragments thereof can be ligated to various cloning vehicles or vectors for use in transforming a host cell. The vectors preferably contains DNA sequences to initiate, control and terminate transcription and translation (which together comprise expression) of the PRV glycoprotein genes and are, therefore, operatively linked thereto. These "expression control sequences" are preferably compatible with the host cell to be transformed. The vectors additionally preferably contain a marker gene (e.g., antibiotic resistance) to provide a phenotypic trait for selection of transformed host cells. Additionally a replicating vector will contain a replicon. Typical vectors are plasmids, phages, and viruses that infect animal cells. In essence, one can use any DNA sequence that is capable of transforming a host cell. The term host cell as used herein means a cell capable of being transformed with the DNA sequence coding for a polypeptide displaying PRV glycoprotein antigenicity. Preferably, the host cell is capable of expressing the PRV polypeptide or fragments thereof. The host cell can be procaryotic or eucaryotic. Illustrative procaryotic cells are bacteria such as E. coli, B. subtilis, Pseudomonas, and B. stearothermophilus. Illustrative eucaryotic cells are yeast or higher animal cells such as cells of insect, plant or mammalian origin. Mammalian cell systems often will be in the form of monolayers of cells although mammalian cell suspensions may also be used. Mammalian cell lines include, for example, VERO and HeLa cells, Chinese hamster ovary (CHO) cell lines, W138, BHK, COS-7 or MDCK cell lines. Insect cell lines include the Sf9 line of Spodoptera frugiperda (ATCC CRL1711). A summary of some available eucaryotic plasmids, host cells and methods for employing them for cloning and expressing PRV glycoproteins can be found in K. Esser, et al., Plasmids of Eukaryotes (Fundamentals and Applications), Springer-Verlag (1986) which is incorporated herein by reference. As indicated above, the vector, e.g., a plasmid, which is used to transform the host cell preferably contains compatible expression control sequences for expression of the PRV glycoprotein gene or fragments thereof. The expression control sequences are, therefore, operatively linked to the gene or fragment. When the host cells are bacteria, illustrative useful expression control sequences include the trp promoter and operator (Goeddel, et al., Nucl. Acids Res., 8, 4057 (1980)); the lac promoter and operator (Chang, et al., Nature, 275, 615 (1978)); the outer membrane protein promoter (EMBO J., 1, 771-775 (1982)); the bacteriophage λ promoters and operators (Nucl. Acids Res., 11, 4677-4688 (1983)); the α-amylase (B. subtilis) promoter and operator, termination sequences and other expression enhancement and control sequences compatible with the selected host cell. When the host cell is yeast, illustrative useful expression control sequences include, e.g., α-mating factor. For insect cells the polyhedrin promoter of baculoviruses can be used (Mol. Cell. Biol., 3, pp. 2156-65 (1983)). When the host cell is of insect or mammalian origin illustrative useful expression control sequences include, e.g., the SV-40 promoter (Science, 222, 524-527 (1983)) or, e.g., the metallothionein promoter (Nature, 296, 39-42 (1982)) or a heat shock promoter (Voellmy, et al., Proc. Natl. Acad. Sci. USA, 82, pp. 4949-53 (1985)). The plasmid or replicating or integrating DNA material containing the expression control sequences is cleaved using restriction enzymes, adjusted in size as necessary or desirable, and ligated with the PRV glycoprotein gene or fragments thereof by means well known in the art. When yeast or higher animal host cells are employed, polyadenylation or terminator sequences from known yeast or mammalian genes may be incorporated into the vector. For example, the bovine growth hormone polyadenylation sequence may be used as set forth in European publication number 0 093 619 and incorporated herein by reference. Additionally gene sequences to control replication of the host cell may be incorporated into the vector. The host cells are competent or rendered competent for transformation by various means. When bacterial cells are the host cells they can be rendered competent by treatment with salts, typically a calcium salt, as generally described by Cohen, PNAS, 69, 2110 (1972). A yeast host cell generally is rendered competent by removal of its cell wall or by other means such as ionic treatment (J. Bacteriol., 153, 163-168 (1983)). There are several well-known methods of introducing DNA into animal cells including, e.g., calcium phosphate precipitation, fusion of the recipient cells with bacterial protoplasts containing the DNA, treatment of the recipient cells with liposomes containing the DNA, and microinjection of the DNA directly into the cells. The transformed cells are grown up by means well known in the art (Molecular Cloning, Maniatis, T., et al., Cold Spring Harbor Laboratory, (1982); Biochemical Methods In Cell Culture And Virology, Kuchler, R. J., Dowden, Hutchinson and Ross, Inc., (1977); Methods In Yeast Genetics, Sherman, F., et al., Cold Spring Harbor Laboratory, (1982)) and the expressed PRV glycoprotein or fragment thereof is harvested from the cell medium in those systems where the protein is excreted from the host cell, or from the cell suspension after disruption of the host cell system by, e.g., mechanical or enzymatic means which are well known in the art. As noted above, the amino acid sequences of the PRV glycoproteins as deduced from the gene structures are set forth in Charts A-C. Polypeptides displaying PRV glycoprotein antigenicity include the sequences set forth in Chart A-C and any portions of the polypeptide sequences which are capable of eliciting an immune response in an animal, e.g., a mammal, which has been injected with the polypeptide sequence and also immunogenically functional analogs of the polypeptides. As indicated hereinabove the entire gene coding for the PRV glycoprotein can be employed in constructing the vectors and transforming the host cells to express the PRV glycoprotein, or fragments of the gene coding for the PRV glycoprotein can be employed, whereby the resulting host cell will express polypeptides displaying PRV antigenicity. Any fragment of the PRV glycoprotein gene can be employed which results in the expression of a polypeptide which is an immunogenic fragment of the PRV glycoprotein or an analog thereof. As is well known in the art, the degeneracy of the genetic code permits easy substitution of base pairs to produce functionally equivalent genes and fragments thereof encoding polypeptides displaying PRV glycoprotein antigenicity. These functional equivalents also are included within the scope of the invention. Charts D-S are set forth to illustrate the constructions of the Examples. Certain conventions are used to illustrate plasmids and DNA fragments as follows: (1) The single line figures represent both circular and linear double-stranded DNA. (2) Asterisks (*) indicate that the molecule represented is circular. Lack of an asterisk indicates the molecule is linear. (3) Endonuclease restriction sites of interest are indicated above the line. (4) Genes are indicated below the line. (5) Distances between genes and restriction sites are not to scale. The figures show the relative positions only unless indicated otherwise. Most of the recombinant DNA methods employed in practicing the present invention are standard procedures, well known to those skilled in the art, and described in detail, for example, in Molecular Cloning, T. Maniatis, et al., Cold Spring Harbor Laboratory, (1982) and B. Perbal, A Practical Guide to Molecular Cloning, John Wiley & Sons (1984), which are incorporated herein by reference. EXAMPLE 1 In this example we set forth the sequencing, cloning and expression of PRV glycoprotein gp50. 1. Sequencing of the gp50 Gene The BamHI 7 fragment of PRV Rice strain DNA (Chart D) which encodes the gp50 gene is isolated from pPRXh1 [NRRL B-15772], supra., and subcloned into the BamHI site of plasmid pBR322 (Maniatis et al., supra.). Referring now to Chart E, the fragment is further subcloned using standard procedures by digesting BamHI 7 with PvuII, isolating the two BamHI/PvuII fragments (1.5 and 4.9 kb) and subcloning them between the BamHI and PvuII sites of pBR322 to produce plasmids pPR28-4 and pPR28-1 incorporating the 1.5 and 4.9 kb fragments respectively (see also, Rea et al., supra.). These subclones are used as sources of DNA for DNA sequencing experiments. Chart F shows various restriction enzyme cleavage sites located in the gp50 gene and flanking regions. The 1.5 and 4.9 kb fragments subcloned above are digested with these restriction enzymes. Each of the ends generated by the restriction enzymes is labeled with τ- 32 P-ATP using polynucleotide kinase and sequenced according to the method of Maxam and Gilbert, Methods Enzymol., 65, 499-560 (1980). The entire gene is sequenced at least twice on both strands. The DNA sequence for gp50 is set forth in Chart A. This DNA may be employed to detect animals actively infected with PRV. For example, one could take a nasal or throat swab, and then do a DNA/DNA hybridization by standard methods to detect the presence of PRV. 2. Expression of gp50 Referring now to Chart G, a NarI cleavage site is located 35 base pairs upstream from the gp50 gene initiation codon. The first step in expression is insertion of the convenient BamHI cleavage site at the point of the NarI cleavage site. Plasmid pPR28-4 from above is digested with restriction endonuclease NarI to produce DNA fragment 3 comprising the N-terminus encoding end of the gp50 gene and a portion of the gX gene. BamHI linkers are added to fragment 3 and the fragment is digested with BamHI to delete the gX sequence thus producing fragment 4. The BamHI ends are then ligated to produce plasmid pPR28-4 Nar2. Referring now to Chart H, we show the assembly of the complete gp50 gene. pPR28-4 Nar2 is digested with BamHI and PvuII to produce fragment 5 (160 bp) comprising the N-terminal encoding portion of the gp50 gene. Plasmid pPR28-1 from above is also digested with PvuII and BamHI to produce a 4.9 kb fragment comprising the C-terminal encoding portion of the gp50 gene (fragment 6). Plasmid pPGX1 (constructed as set forth in U.S. patent application SN 760,130)), or, alternatively, plasmid pBR322, is digested with BamHI, treated with bacterial alkaline phosphatase (BAP) and then ligated with fragments 5 and 6 to produce plasmid pBGP50-23 comprising the complete gp50 gene. Referring now to Chart I, we show the production of plasmid pD50. Plasmid pBG50-23 is cut with restriction enzyme MaeIII (K. Schmid et al., Nucl. Acids Res. , 12, p. 2619 (1984)) to yield a mixture of fragments. The MaeIII ends are made blunt with T4 DNA polymerase and EcoRI linkers are added to the blunt ends followed by EcoRI digestion. The resulting fragments are cut with BamHI and a 1.3 kb BamHI/EcoRI fragment containing the gp50 gene (fragment 7) is isolated. Plasmid pSV2dhfr (obtained from the American Type Culture Collection, Bethesda Research Laboratories, or synthesized according to the method of S. Subramani, et al., Mol. Cell. Biol., 2, pp. 854-64 (1981)) is digested with BamHI and EcoRI and the larger (5.0 kb) fragment is isolated to produce fragment 8 containing the dihydrofolate reductase (dhfr) marker. Fragments 7 and 8 are then ligated to produce plasmid pD50 comprising the gp50 gene and the dhfr marker. Referring now to Chart J, the immediate early promoter from human cytomegalovirus Towne strain is added upstream from the gp50 gene. pD50 is digested with BamHI and treated with bacterial alkaline phosphatase to produce fragment 9. A 760 bp Sau3A fragment containing the human cytomegalovirus (Towne) immediate early promoter is isolated according to the procedure set forth in U.S. patent application SN 758,517 to produce fragment 10 (see also, D.R. Thomsen, et al., Proc. Natl. Acad. Sci. USA, 81, pp. 659-63 (1984)). These fragments are then ligated by a BamHI/Sau3A fusion to produce plasmid pDIE50. To confirm that the promoter is in the proper orientation to transcribe the gp50 gene the plasmid is digested with SacI and PvuII and a 185 bp fragment is produced. Referring now to Chart K, the 0.6 kb PvuII/EcoRI fragment containing the bovine growth hormone polyadenylation signal is isolated from plasmid pGH2R2 (R.P. Woychik, et al., Nucl. Acids Res., 10, pp. 7197-7210 (1982) by digestion with PvuII and EcoRI or from pSVCOW7 (supra.) to produce fragment 11. Fragment 11 is cloned between the EcoRI and SmaI cleavage sites of pUC9 (obtained from Pharmacia/PL or ATCC) to give pCOWT1. pCOWT1 is cut with SalI, the ends made blunt with T4 DNA polymerase, EcoRI linkers are added, the DNA is cut with EcoRI, and the 0.6 kb fragment (fragment 12) is isolated. This is the same as fragment 11 except that it has two EcoRI ends and a polylinker sequence at one end. Plasmid pDIE50 is cut with EcoRI, and fragment 12 is cloned into it to produce plasmid pDIE50PA. Digestion with BamHI and PvuII produces a fragment of 1.1 kb in the case where the polyadenylation signal is in the proper orientation. The plasmid can also be constructed by cloning in the polyadenylation sequence before the promoter. Plasmid pDIE50PA is used to transfect CHO dhfr - cells (DXB-11, G. Urlaub and L.A. Chasin, Proc. Natl. Acad. Sci. USA, 77, pp. 4216-20 (1980)) by calcium phosphate co-precipitation with salmon sperm carrier DNA (F.L. Graham and A.J. Van Der Eb, Virol., 52, pp. 456-67 (1973)). The dihydrofolate reductase positive (dhfr + ) transfected cells are selected in Dulbecco's modified Eagle's medium plus Eagle's non-essential amino acids plus 10% fetal calf serum. Selected dhfr + CHO cells produce gp50 as detected by immunofluorescence with anti-gp50 monoclonal antibody 3A-4, or by labelling with 14 C-glucosamine and immunoprecipitation with 3A-4. Monoclonal antibody 3A-4 is produced as described in copending U.S. patent application SN 817,429, filed January 9, 1985. Immunoprecipitation reactions are performed as described previously (T.J. Rea, et al., supra.) except for the following: The extracts are first incubated with normal mouse serum, followed by washed Staphylococcus aureus cells, and centrifuged for 30 minutes in a Beckman SW50.1 rotor at 40,000 rpm. After extracts are incubated with monoclonal or polyclonal antiserum plus S. Aureus cells, the cells are washed three times in 10 mM Tris HCl, pH 7.0, 1 mM EDTA, 0.1 M NaCl, 1% NP40 and 0.5% deoxycholate. Analysis of proteins is done on 11% SDS polyacrylamide gels (L. Morse, et al., J. Virol., 26, pp. 389-410 (1984)). In preliminary immunofluorescence assays it was found that 3A-4 reacted with the pDIE50PA-transfected CHO cells but not with untransfected CHO cells. When the transfected CHO cells were labelled with 14 C-glucosamine, 3A-4 immunoprecipitated a labelled protein from cells containing pDIE50PA but not from control cells making human renin. The precipitated protein co-migrated on SDS-polyacrylamide gels with the protein precipitated by 3A-4 from PRV-infected cells. A clone of these transfected CHO cells producing gp50 can be grown in roller bottles, harvested in phosphate buffered saline plus 1 mM EDTA, and mixed with complete Freund's adjuvant for use as a vaccine. The gp50 gene can also be expressed in a vaccinia vector. In this embodiment, after pBG50-23 is digested with MaeIII and the ends made blunt with T4 DNA polymerase, the DNA is digested with BamHI. The 1.3 BamHI/blunt-ended fragment containing the gp50 gene is isolated. Plasmid pGS20 (Mackett, et al., J. Virol., 49, pp. 857-64 (1984)) is cut with BamHI and SmaI, and the larger 6.5 kb fragment is isolated by gel electrophoresis. These two fragments are ligated together to produce pVV50. Plasmid pVV50 is transfected into CV-1 cells (ATCC CCL 70) infected with the WR strain of vaccinia virus (ATCC VR-119), and selected for thymidine kinase negative recombinants by plating on 143 cells (ATCC CRL 8303) in 5-bromodeoxy-uridine (BUdR) by the methods described by Mackett, et al. in DNA Cloning, Volume II: A Practical Approach, D.M. Glover, ed., IRL Press, Oxford (1985). The resulting virus, vaccinia-gp50, expressed gp50 in infected cells, as assayed by labelling of the proteins of the infected cell with 14 C-glucosamine and immunoprecipitation with monoclonal antibody 3A-4. EXAMPLE 2 In this example we set forth the protection of mice and swine from PRV challenge using the gp50 of Example 1 as an immunogenic agent. In Tables 1-3, infra, the microneutralization assay was done as follows: Serial two-fold dilutions of serum samples were done in microtiter plates (Costar) using basal medium Eagle (BME) supplemented with 3% fetal calf serum and antibiotics. About 1000 pfu (50 µl) of PRV were added to 50 µl of each dilution. Rabbit complement was included in the virus aliquot at a dilution of 1:5 for the mouse serum assays but not the pig serum assays. The samples were incubated for either 1 hr (swine sera) or 3 hrs (mouse sera) at 37°C. After the incubation period, an aliquot (50 µl) of porcine kidney-15 (PK-15) cells (300,000 cells/ml) in Eagle's Minimum Essential Medium was added to each serum per PRV sample. The samples were subsequently incubated at 37°C for 2 days. Neutralizing titers represent the reciprocals of the highest dilutions which protected 50% of the cells from cytopathic effects. Table 1 sets forth the protection of nice from challenge by virulent PRV by immunization with gp50 produced in vaccinia virus. Mice were immunized by tail scarification with 25 µl or by the footpad route with 50 µl. Mice were immunized 28 days prior to challenge (except mice given PR-Vac which were immunized 14 days prior to challenge). Immunizing Agent Dose (PFU) Route Neutralizing Titers % Survival gp50 3.0x10 7 Tail 1024 93 gp50 6.0x10 7 Footpad 1024 100 gp50 7.5x10 6 Tail 512 93 vaccinia 7.5x10 6 Tail <8 27 BME -- Tail <8 20 PR-Vac -- Footpad 512 90 Table 2 sets forth the protection of mice from challenge by virulent PRV by immunization with gp50 produced in CHO cells. Mice were immunized at 28 days, 18 days and 7 days prior to challenge. Mice received preparations with adjuvants subcutaneously on the first dose and preparations in saline intraperitoneally on the second and third doses. Each mouse received 10 6 disrupted cells/dose. Immunizing Agent/Adjuvant Neutralizing Titers % Survival gp50/CFA 512 100 (10/10) gp50/CFA (2 doses) ND 80 (4/5) gp50/IFA 1024 90 (9/10) gp50/saline 256 100 (3/3) CHO-renin /CFA <8 10 (1/10) Nontreated <8 0 (0/10) PR-Vac 4096 90 (9/10) Table 3 sets forth the protection of swine from challenge by virulent PRV by immunization with gp50 produced in CHO cells. Swine were immunized at 21 days and 7 days prior to challenge. Swine received 2x10 7 disrupted cells per dose. The first dose was mixed with complete Freund's adjuvant while the second dose was suspended in saline. Both doses were given intramuscularly. Immunizing Agent/Adjuvant Geometric Mean Titer % Survival gp50/CFA 25 100 CHO-renin/CFA <8 0 These three tables demonstrate that gp50 can raise neutralizing antibodies and protect mice and swine from lethal PRV challenge. In another aspect of the instant invention we produced a derivative of glycoprotein gp50 by removing the DNA coding for the C-terminal end of gp50. The resulting polypeptide has a deletion for the amino acid sequence necessary to anchor gp50 into the cell membrane. When expressed in mammalian cells this gp50 derivative is secreted into the medium. Purification of this gp50 derivative from the medium for use as a subunit vaccine is much simpler than fractionation of whole cells. Removal of the anchor sequence to convert a membrane protein into a secreted protein was first demonstrated for the influenza hemagglutinin gene (M.-J. Gething and J. Sambrook, Nature, 300, pp. 598-603 (1982)). Referring now to Chart L, plasmid pDIE50 from above is digested with SalI end EcoRI. The 5.0 and 0.7 kb fragments are isolated. The 0.7 kb fragment encoding a portion of gp50 is digested with Sau3A end a 0.5 kb SalI/Sau3A fragment is isolated. To introduce a stop codon after the truncated gp50 gene, the following oligonucleotides are synthesized: The 5.0 kb EcoRI/SalI fragment, the 0.5 kb SalI/Sau3A fragment and the annealed oligonucleotides are ligated to produce plasmid pDIE50T. Digestion with EcoRI and SalI produces a 580 bp fragment. pDIE50T is cut with EcoRI and the 0.6 kb EcoRI fragment containing the bGH polyA site (fragment 12) is cloned in to produce plasmid pDIE50TPA. Digestion of pDIE50TPA with BamHI and PvuII yields a 970 bp fragment when the polyadenylation signal is in the proper orientation. pDIE50TPA is used to transfect CHO dhfr - cells. Selected dhfr + CHO cells produce a truncated form of gp50 which is secreted into the medium as detected by labelling with 35 S-methionine and immunoprecipitation. EXAMPLE 3 In this example we set forth the isolation, cloning and sequencing of the gp63 and gI genes. 1. Library Construction PRV genomic DNA was prepared as described previously (T.J. Rea, et al., supra.). Fragments of 0.5-3.0 kb were obtained by sonicating the PRV genomic DNA of the PRV Rice strain twice for 4 sec each time at setting 2 with a Branson 200 sonicator. After blunt ending the fragments with T4 DNA polymerase, the fragments were ligated to kinased EcoRI linkers (T. Maniatis, et al., supra). After over-digestion with EcoRI (since PRV DNA does not contain an EcoRI site, methylation was unnecessary), excess liners were removed by agarose gel electrophoresis. The PRV DNA fragments in the desired size range were eluted by the glass slurry method, (B. Vogelstein and D. Gillespie, Proc. Natl. Acad. Sci. USA, 76, pp. 615-19 (1979)). A library of 61,000 λ/PRV recombinants (λPRVs) was constructed by ligating 500 ng of PRV DNA fragments to 750 ng of EcoRI digested λgt11 (R.A. Young and R.W. Davis, supra.) DNA in 50 mM Tris (pH 7.4), 10 mM MgCl 2 , 10 mM dithiothreitol, 1 mM spermidine, 1 mM ATP, 400 units of T4 DNA ligase (New England Biolabs), in a final volume of 10 µl. The ligated DNA was packaged into bacteriophage λ virions using the Packagene extract (Promega Biotec, Madison, Wisconsin). 2. λPRV Library Screening The λPRV library was screened as previously described (J.G. Timmins, et al., supra.; R.A. Young and R.W. Davis, supra.). 20,000 phages were screened per 150 mm LB-ampicillin plate. The screening antisera were raised by injecting mice with size fractions of PRV infected cell proteins (ICP's) eluted from SDS-polyacrylamide gels (J.G. Timmins, et al., supra.). Plaques giving positive signals upon screening with antisera were picked from the agar plates with a sterile pasteur pipette, resuspended in 1 ml SM buffer (T. Maniatis, et al., supra) and rescreened. The screening was repeated until the plaques were homogeneous in reacting positively. Approximately 43,000 λPRV recombinants were screened with mouse antisera to PRV infected Vero cell proteins, isolated from SDS-polyacrylamide gels. Sixty positive λPRV phages were isolated. 3. Phage Stock Preparation High titer phage stocks (10 10 -10 11 pfu/ml) were prepared by the plate lysate method (T. Maniatis et al., supra). A single, well-isolated positive signal plaque was picked and resuspended in 1 ml SR. 100 µl of the suspension was adsorbed to 300 µl of E. coli Y1090 (available from the American Type Culture Collection (ATCC), Rockville, Maryland) at 37°C for 15 min, diluted with 10 ml LB-top agarose, poured evenly on a 150 mm LB-ampicillin plate and incubated overnight at 42°C. The top agarose was gently scraped off with a flamed glass slide and transferred to a 30 ml Corex tube. 8 ml of SM and 250 µl of chloroform were added, mixed and incubated at 37°C for 15 min. The lysate was clarified by centrifugation at 10,000 rpm for 30 min in the HB-4 rotor. The phage stock was stored at 4°C with 0.3% chloroform. 4. Fusion Protein Preparation and Analysis LB medium (Maniatis, et al., supra.) was inoculated 1:50 with a fresh overnight culture of E. coli K95 (sup - , λ - , gal - , str r , nusA - ; D. Friedman, supra.) and grown to an OD 550 = 0.5 at 30°C. 25 ml of culture was infected with λPRV phage at a multiplicity of 5 and incubated in a 42°C shaking water bath for 25 min, followed by transfer to 37°C for 2-3 hours. The cells were pelleted at 5,000 rpm for 10 min in the HB-4 rotor and resuspended in 100 µl of 100 mM Tris (pH 7.8), 300 mM NaCl. An equal volume of 2x SDS-PAGE sample buffer was added, and the sample was boiled for 10 min. 5 µl of each sample was analyzed by electrophoresis on analytical SDS-polyacrylamide gels as described in L. Morse et al., J. Virol, 26, pp. 389-410 (1978). The fusion polypeptide preparations were scaled up 10-fold for mouse injections. The β-galactosidase/PRV fusion polypeptides were isolated after staining a strip of the gel with coomassie blue (L. Morse et al., supra; K. Weber and M. Osborn, in The Proteins, 1, pp. 179-223 (1975)). Fusion polypeptide quantities were estimated by analytical SDS-PAGE. Cell lysates from λPRV infected E. coli K95 cultures were electrophoresed in 9.25% SDS-polyacrylamide gels. Overproduced polypeptide bands with molecular weights greater than 116,000 daltons, absent from λgt11-infected controls, were β-galactosidase-PRV fusion polypeptides. The β-galactosidase-PRV fusion polypeptides ranged in size from 129,000 to 158,000 daltons. Approximately 50-75 µg of fusion polypeptide was resuspended in complete Freund's adjuvant and injected subcutaneously and interperitoneally per mouse. Later injections were done intraperitoneally in incomplete Freund's adjuvant. 5. Antisera Analysis Immunoprecipitations of 14 C-glucosamine ICP's, 35 S-methionine ICP's and 14 C-glucosamine gX were done as previously described (T.J. Rea, et al., supra.). These techniques showed that gp63 and gI had been isolated in a λgt11 recombinant phage. We called these phages λ37 and λ36 (gp63) and λ23 (gI). 6. λDNA Mini-preps Bacteriophage were rapidly isolated from plate lysates (T. J.-Silhavy et al., Experiments With Gene Fusions, (1984)). 5% and 40% glycerol steps (3 ml each in SM buffer) were layered in an SW41 tube. A plate lysate (∼6 ml) was layered and centrifuged at 35,000 rpm for 60 min at 4°C. The supernatant was discarded and the phage pellet was resuspended in 1 ml SM. DNAse I and RNAse A were added to final concentrations of 1 µg/ml and 10 µg/ml. After incubation at 37°C for 30 min, 200 µl of SDS Mix (0.25 M EDTA, 0.5 M Tris (pH 7.8), 2.5% SDS) and proteinase K (to 1 mg/ml) were added and incubated at 68°C for 30 min. The λDNA was extracted with phenol three times, extracted with chloroform, and ethanol precipitated. An average 150 mm plate lysate yields 5-10 µg of λDNA. 7. λPRV DNA Analysis PRV DNA was digested to completion with BamHI and KpnI, electrophoresed in 0.8% agarose and transferred to nitrocellulose by the method of Southern (J. Mol. Biol., 98, pp. 503-17 (1975)). The blots were sliced into 4 mm strips and stored desiccated at 20-25°. λPRV DNAs were nick-translated (Amersham) to specific activities of approximately 10 8 cpm/µg. Pre-hybridization was done in 6x SSC, 30% formamide, 1x Denhardt's reagent (0.02% each of ficoll, polyvinylpyrrolidone and bovine serum albumin), 0.1% SDS, 50 µg/ml heterologous DNA at 70°C for 1 hour. Hybridization was done in the same solution at 70°C for 16 hours. Fifteen minute washes were done twice in 2x SSC, 0.1% SDS and twice in 0.1x SSC, and 0.1% SDS, all at 20-25°. The blots were autoradiographed with an intensifying screen at ∼70°C overnight. By Southern blotting the PRV glycoprotein genes contained in λ23, λ36 and λ37 mapped to the BamHI 7 fragment in the unique small region (see T.J. Rea, et al., supra.). Finer mapping of this fragment showed that λ23 (gI) gene mapped distal to the gX gene and that λ37 mapped to the internal region of BamHI 7, as shown in Chart D. 8. Sequencing The gp63 and gI Genes The PRV DNA in λ36 and λ37 was determined to contain a StuI cleavage site. There is only one StuI cleavage site in the BamHI 7 fragment; therefore, the open reading frame that included the StuI cleavage site was sequenced. Chart E shows various restriction enzyme cleavage sites located in the gp63 gene and flanking regions. BamHI 7 was subcloned and digested with these restriction enzymes. Each of the ends generated by the restriction enzymes was labeled with γ- 32 P-ATP using polynucleotide kinase and sequenced according to the method of Maxam and Gilbert, Methods Enzymol., 65, 499-560 (1980). Plasmid pPR28 is produced by cloning the BamHI 7 fragment isolated from pUC1129 into plasmid pSV2 gpt (R.C. Mulligan and P. Berg, Proc. Natl. Acad. Sci. USA, 78, pp. 2072-76 (1981)). Plasmid pPR28-1 was produced by digesting pPR28 with PvuII and then recircularizing the piece containing the E. coli origin of replication and bla gene to produce a plasmid comprising a 4.9 kb PvuII/BamHI 7 PRV fragment containing the DNA sequence for gI. Chart N shows various restriction enzyme cleavage sites located In the gI gene and flanking regions. BamHI 7 was subcloned, digested, labeled and sequenced as set forth above. The DNA sequences for glycoproteins gp63 and gI are set forth in Charts B and C respectively. This DNA may be employed to detect animals actively infected with PRV. For example, one could take a nasal or throat swab, and then by standard DNA/DNA hybridization methods detect the presence of PRV. EXAMPLE 4 In this example we set forth the expression of gI in mammalian cells. A BamHI 7 fragment containing the gI gene is isolated from plasmid pPR28 (see above) by digesting the plasmid with BamHI, separating the fragments on agarose gel and then excising the fragment from the gel. Referring now to Chart O, the BamHI 7 fragment isolated above is then cloned into plasmid pUC19 (purchased from Pharmacia/PL) to produce plasmid A. Plasmid A is digested with DraI. DraI cleaves the pUC19 sequence in several places, but only once in the BamHI 7 sequence between the gp63 and gI genes (Chart D) to produce, inter alia, fragment 1. BamHI linkers are ligated onto the DraI ends of the fragments, including fragment 1, and the resulting fragment mixture is digested with BamHI. The product fragments are separated by agarose gel electrophoresis and fragment 2 (2.5 kb) containing the gI gene is purified. Fragment 2 is cloned into pUC19 digested with BamHI to produce plasmid pUCD/B. Of the two plasmids so produced, the plasmid containing the gI gene in the proper orientation is determined by digesting the plasmids with BsmI and EcoRI; the plasmid in the proper orientation contains a characteristic 750 bp BsmI/EcoRI fragment. Referring now to Chart P, plasmid pUCD/B (Chart O) is digested with BsmI and EcoRI and the larger fragment (fragment 3, 4.4 kb) is purified by agarose gel electrophoresis. The following two oligonucleotides are synthesized chemically by well-known techniques or are purchased from a commercial custom synthesis service: These oligonucleotides are ligated to fragment 3 to replace the coding sequence for the C-terminus of the gI gene which was deleted by the BsmI cleavage. The resulting plasmid, pGI, contains a complete coding region of the gI gene with a BamHI cleavage site upstream and an EcoRI cleavage site downstream from the gI coding sequences. Plasmid pGI is digested with EcoRI and BamHI and a 1.8 kb fragment comprising the gI gene (fragment 4) is purified on an agarose gel. Plasmid pSV2dhfr, (supra.) is cut with EcoRI, and is then cut with BamHI to produce fragment 5 (5.0 kb) containing the dhfr marker, which is isolated by agarose gel electrophoresis. Then fragments 4, and 5 are ligated to produce plasmid pDGI which comprises the dihydrofolate reductase and ampicillin resistance markers, the SV40 promoter and origin of replication, and the gI gene. Referring now to Chart Q, the immediate early promoter from human cytomegalovirus Towne strain is added upstream from the gI gene. Plasmid pDGI is digested with BamHI to produce fragment 6. The human cytomegalovirus (Towne) immediate early promoter is isolated (supra.) to produce fragment 7. Fragments 6 and 7 are then ligated to produce plasmid pDIEGIdhfr. To confirm that the promoter is in the proper orientation the plasmid is digested with SacI and BstEII restriction enzymes. The production of an about 400 bp fragment indicates proper orientation. A 0.6 kb PvuII/EcoRI fragment containing the bovine growth hormone polyadenylation signal is isolated from the plasmid pSVCOW7 (supra.) to produce fragment 8. Fragment 8 is cloned across the SmaI/EcoRI sites of pUC9 (supra.) to produce plasmid pCOWT1. pCOWT1 is cut with SalI, treated with T4 DNA polymerase, and EcoRI linkers are ligated on. The fragment mixture so produced is then digested with EcoRI and a 0.6 kb fragment is isolated (fragment 9). Fragment 9 is cloned into the EcoRI site of pUC19 to produce plasmid pCOWT1E. pCOWT1E is digested with EcoRI to produce fragment 10 (600 bp). Plasmid pDIEGIdhfr is digested with EcoRI and ligated with fragment 10 containing the bGH polyadenylation signal to produce plasmid pDIEGIPA. The plasmid having the gI gene in the proper orientation is demonstrated by the production of a 1400 bp fragment upon digestion with BamHI and BstEII. The resulting plasmid is transfected into dhfr - Chinese hamster ovary cells and dhfr + cells are selected to obtain cell lines expressing gI (Subramani, et al, Mol. Cell Biol., 1, pp.854-64 (1981)). The expression of gI is amplified by selecting clones of transfected cells that survive growth in progressively higher concentrations of methotrexate (McCormick, et al, Mol. Cell Biol., 4, pp. 166-72 (1984). EXAMPLE 5 In this example we set forth the expression of gp63 in mammalian cells. The BamHI 7 fragment of PRV DNA (supra.) is isolated from pPRXh1 [NRRL B-15772], and subcloned into the BamHI site of plasmid pBR322 as in Example 1 for use in sequencing and producing more copies of the gp63 gene. Referring now to Chart R, from within BamHI 7 a 1.9 kb BstEII/KpnI fragment (fragment 1) is subcloned by cutting BamHI 7 with BstEII, treating the ends with T4 DNA polymerase, and then cutting with KpnI. Fragment 1 is isolated and cloned between the KpnI and SmaI sites in pUC19 (purchased from Pharmacia/PL, Piscataway, NJ) to yield plasmid pPR28-1BK. Plasmid pPR28-1BK is cut with DraI plus MaeIII to yield fragment 2 (1.1 kb). The DraI cleavage site is outside the coding region of the gp63 gene and downstream from its polyadenylation signal. The MaeIII cleavage site cuts 21 bases downstream from the ATG initiation codon of the gp63 gene. To replace the coding region removed from the gp63 gene, the following two oligonucleotides are synthesized chemically or purchased from commercial custom synthesis services (fragment 4): Plasmid pSV2dhfr, supra., is cut with EcoRI, treated with T4 DNA polymerase, then cut with BamHI and the larger (5.0 kb) fragment is isolated to produce fragment 4 containing the dhfr marker. Then fragments 2, 3, and 4 are ligated to produce plasmid pGP63dhfr. Referring now to Chart S, the immediate early promoter from human cytomegalovirus Towne strain is added upstream from the gp63 gene. pGP63dhfr is digested with BamHI and treated with bacterial alkaline phosphatase to produce fragment 5. A 760 bp Sau3A fragment containing human cytomegalovirus (Towne) immediate early promoter is isolated to produce fragment 6. These fragments are then ligated to produce plasmid pIEGP63dhfr. To confirm that the promoter is in the proper orientation the plasmid is digested with SacI and PvuII and a 150 bp fragment is produced. The resulting plasmid is transfected into dhfr - Chinese hamster ovary cells and dhfr + cells are selected to obtain cell lines expressing gp63. Since the levels of synthesis of gp63 by this system were too low to detect by the methods we used, we produced the polypeptide in vaccinia virus as set forth below. EXAMPLE 6 In this example we set forth the expression of gp63 in vaccinia virus. The method used herein incorporates aspects of other syntheses referred to above. Fragments 1, 2, 3, and 4 are produced according to Example 5. Plasmid pGS20 (Mackett, et al., J. Virol., 49, pp. 857-64 (1984)) is cut with BamHI and SmaI, and the larger 6.5 kb fragment is isolated by gel electrophoresis. Fragment 2, the oligonucleotides, and the pGS20 fragment are ligated together to produce plasmid pVV63. This plasmid is transfected into CV-1 cells (ATCC CCL 70) infected with the WR strain of vaccinia virus (ATCC VR-119), selected for thymidine kinase negative recombinants by plating on 143 cells (ATCC CRL 8303) in BUdR by the methods described by Mackett, et al. in DNA Cloning, Volume II: A Practical Approach, D.M. Glover, ed., IRL Press, Oxford (1985). The resulting virus, vaccinia-gp63, expresses gp50 in infected cells, as assayed by labelling of the proteins of the infected cell with 14 C-glucosamine and immunoprecipitation with anti-gp63 antiserum. The BamHI/EcoRI fragment from plasmid pGI, the DraI/MaeIII fragment from plasmid pPR28-1BK, or the BamHI/MaeIII fragment from pBGP50-23 all described above, may also be treated with Bal31 and inserted in pTRZ4 (produced as set forth in copending U.S. patent application SN 606,307) as described in Rea, et al., supra., and used to transform E. coli. By this method, gp50, gp63, and gI can be produced as a fusion protein in E. coli. Also, by substituting, for example, pSV2neo (available from the American Type Culture Collection) for pSV2dhfr in the above example, the recombinant plasmid comprising the PRV glycoprotein gene could be transformed into other host cells. Transformed cells would be selected by resistance to antibiotic G418 which is encoded by the plasmid. One can also express the polypeptides of the instant invention in insect cells as follows: By putting a BamHI linker on the EcoRI site of pD50 and digestion with BamHI, or putting a BamHI linker on the EcoRI site of pGP63dhfr and digestion with BamHI, or by digestion of pUCD/B with BamHI, one obtains BamHI fragments containing the gp50, gp63, or gI genes respectively. These BamHI fragments can be cloned into a BamHI site downstream from a polyhedrin promoter in pAC373 (Mol. Cell. Biol., 5, pp. 2860-65 (1985)). The plasmids so produced can be co-transfected with DNA from baculovirus Autographa californica into Sf9 cells, and recombinant viruses isolated by methods set forth in the article. These recombinant viruses produce gp50, gp63, or gI upon infecting Sf9 cells. A vaccine prepared utilizing a glycoprotein of the instant invention or an immunogenic fragment thereof can consist of fixed host cells, a host cell extract, or a partially or completely purified PRV glycoprotein preparation from the host cells or produced by chemical synthesis. The PRV glycoprotein immunogen prepared in accordance with the present invention is preferably free of PRV virus. Thus, the vaccine immunogen of the invention is composed substantially entirely of the desired immunogenic PRV polypeptide and/or other PRV polypeptides displaying PRV antigenicity. The immunogen can be prepared in vaccine dose form by well-known procedures. The vaccine can be administered intramuscularly, subcutaneously or intranasally. For parenteral administration, such as intramuscular injection, the immunogen may be combined with a suitable carrier, for example, it may be administered in water, saline or buffered vehicles with or without various adjuvants or immunomodulating agents including aluminum hydroxide, aluminum phosphate, aluminum potassium sulfate (alum), beryllium sulfate, silica, kaolin, carbon, water-in-oil emulsions, oil-in-water emulsions, muramyl dipeptide, bacterial endotoxin, lipid X, Corynebacterium parvum (Propionobacterium acnes), Bordetella pertussis, polyribonucleotides, sodium alginate, lanolin, lysolecithin, vitamin A, saponin, liposomes, levamisole, DEAE-dextran, blocked copolymers or other synthetic adjuvants. Such adjuvants are available commercially from various sources, for example, Merck Adjuvant 65 (Merck and Company, Inc., Rahway, N.J.). Another suitable adjuvant is Freund's Incomplete Adjuvant (Difco Laboratories, Detroit, Michigan). The proportion of immunogen and adjuvant can be varied over a broad range so long as both are present in effective amounts. For example, aluminum hydroxide can be present in an amount of about 0.5% of the vaccine mixture (Al 2 O 3 basis). On a per dose basis, the concentration of the immunogen can range from about 1.0 µg to about 100 mg per pig. A preferable range is from about 100 µg to about 3.0 mg per pig. A suitable dose size is about 1-10 ml, preferably about 1.0 ml. Accordingly, a dose for intramuscular injection, for example, would comprise 1 ml containing 1.0 mg of immunogen in admixture with 0.5% aluminum hydroxide. Comparable dose forms can also be prepared for parenteral administration to baby pigs, but the amount of immunogen per dose will be smaller, for example, about 0.25 to about 1.0 mg per dose. For vaccination of sows, a two dose regimen can be used. The first dose can be given from about several months to about 5 to 7 weeks prior to farrowing. The second dose of the vaccine then should be administered some weeks after the first dose, for example, about 2 to 4 weeks later, and vaccine can then be administered up to, but prior to, farrowing. Alternatively, the vaccine can be administered as a single 2 ml dose, for example, at about 5 to 7 weeks prior to farrowing. However, a 2 dose regimen is considered preferable for the most effective immunization of the baby pigs. Semi-annual revaccination is recommended for breeding animals. Boars may be revaccinated at any time. Also, sows can be revaccinated before breeding. Piglets born to unvaccinated sows may be vaccinated at about 3-10 days, again at 4-6 months and yearly or preferably semi-annually thereafter. The vaccine may also be combined with other vaccines for other diseases to produce multivalent vaccines. It may also be combined with other medicaments, for example, antibiotics. A pharmaceutically effective mount of the vaccine can be employed with a pharmaceutically acceptable carrier or diluent to vaccinate animals such as swine, cattle, sheep, goats, and other mammals. Other vaccines may be prepared according to methods well known to those skilled in the art as set forth, for example, in I. Tizard, An Introduction to Veterinary Immunology, 2nd ed. (1982), which is incorporated herein by reference. As set forth above, commercial vaccine PRV's have been found to have the gI and gp63 genes deleted. Therefore gI and gp63 polypeptides produced by the methods of this invention can be used as diagnostic agents to distinguish between animals vaccinated with these commercial vaccines and those infected with virulent virus. To differentiate between infected and vaccinated animals, one could employ, for example, an ELISA assay. gI or gp63 protein, produced, for example, in E. coli by recombinant DNA techniques (Rea, et al., supra.), is added to the wells of suitable plastic plates and allowed sufficient time to absorb to the plastic (e.g., overnight, 20-25° C). The plates are washed and a blocking agent (e.g., BSA) is added to neutralize any unreacted sites on the plastic surface. A wash follows and then the pig serum is added to the wells. After about 1 hour incubation at 20-25° C, the wells are washed and a protein A-horseradish peroxidase conjugate is added to each well for an about 1 hour incubation a 20-25° C. Another wash follows and the enzyme substrate (o-phenylenediamine) is added to the wells and the reaction is terminated with acid. Absorbency is measured at 492 nanometers to quantitate the amount of gI or gp63 antibody present in the serum. Lack of gI or gp63 indicates that an animal is not infected. By testing for other PRV antigens, one could establish whether or not a given animal was vaccinated.

Claims: Claims for the following Contracting States : BE, CH, DE, FR, GB, GR, IT, LI, LU, NL, SE A recombinant DNA molecule comprising a DNA sequence operatively linked to an expression control sequence, wherein the DNA sequence codes for a polypeptide displaying pseudorabies virus glycoprotein gp50, gp63 or gI immunogenicity, the glycoprotein having the amino-acid sequence shown in Chart A, B or C, respectively, wherein the expression control sequence is not naturally operatively linked to the DNA sequence encoding a polypeptide displaying pseudorabies virus glycoprotein gp50, gp63 or gI immunogenicity. A recombinant DNA molecule of claim 1, wherein the DNA sequence coding for the polypeptide is the nucleotide sequence shown in Chart A, B or C, or a fragment or derivative thereof encoding a polypeptide displaying pseudorabies virus immunogenicity. A recombinant DNA molecule of claim 1 or claim 2, wherein the glycoprotein or nucleotide sequence, respectively, is as shown in Chart C. A host cell transformed with a recombinant DNA molecule according to any preceding claim. A host cell of claim 4 which is of bacterial, fungal, plant or animal origin. A host cell of claim 5 which is E . coli , a yeast cell or a Chinese hamster ovary cell. A method for producing a polypeptide as defined in claim 1, which comprises culturing a host cell according to any of claims 4 to 6. Use of a polypeptide displaying pseudorabies virus glycoprotein gp63 or gI immunogenicity, the glycoprotein having the amino-acid sequence shown in Chart B or C, respectively, for the serological distinction between an animal to which a vaccine pseudorabies virus lacking gp63 or gI has been administered and an animal infected with pseudorabies virus, without sacrificing the animal. Use according to claim 8, wherein the glycoprotein has the sequence shown in Chart C, the virus lacking gI. Use according to claim 8 or claim 9, comprising an enzyme-linked immunosorbent assay. A kit for use in serological distinction as defined in any of claims 8 to 10, which comprises a plurality of containers of which one contains the polypeptide. Claims for the following Contracting States : AT, ES A method for producing a polypeptide displaying pseudorabies virus glycoprotein gp50, gp63 or gI immunogenicity, the glycoprotein having the amino-acid sequence shown in Chart A, B or C, respectively, which comprises culturing a host cell transformed with a recombinant DNA molecule comprising a DNA sequence that codes for the polypeptide and is operatively linked to an expression control sequence, wherein the expression control sequence is not naturally operatively linked to the DNA sequence encoding a polypeptide displaying pseudorabies virus glycoprotein gp50, gp63 or gI immunogenicity. A method of claim 1, wherein the DNA sequence coding for the polypeptide is the nucleotide sequence shown in Chart A, B or C, or a fragment or derivative thereof encoding a polypeptide displaying pseudorabies virus immunogenicity. A method of claim 1 or claim 2, wherein the glycoprotein or nucleotide sequence, respectively, is as shown in Chart C. A method of any preceding claim, wherein the host cell is of bacterial, fungal, plant or animal origin. A method of claim 4, wherein the host cell is E . coli , a yeast cell or a Chinese hamster ovary cell. Use of a polypeptide displaying pseudorabies virus glycoprotein gp63 or gI immunogenicity, the glycoprotein having the amino-acid sequence shown in Chart B or C, respectively, for the serological distinction between an animal to which a vaccine pseudorabies virus lacking gp63 or gI has been administered and an animal infected with pseudorabies virus, without sacrificing the animal. Use according to claim 6, wherein the glycoprotein has the sequence shown in Chart C, the virus lacking gI. Use according to claim 6 or claim 7, comprising an enzyme-linked immunosorbent assay.

Inventors: PETROVSKIS ERIK A, POST LEONARD E, TIMMINS JAMES G, PETROVSKIS, ERIK A., POST, LEONARD E., TIMMINS, JAMES G.
Applicants: UPJOHN CO, THE UPJOHN COMPANY
Application year: 1986
Main classification: C12N15
IPC codes: C07K14, C12P21, C12N15, C12R1, C12N1, G01N33, C12N5, A61K39, A61P31