Physical mapping of the mutation in an antigenic variant of herpes simplex virus type 1 by use of an immunoreactive plaque assay

Analysis of pseudorabies virus glycoprotein gIII localization and modification by using novel infectious viral mutants carrying unique EcoRI sites

We have constructed two pseudorabies virus (PRV) mutants, each with a unique EcoRI restriction site in the nonessential gIII envelope glycoprotein gene. Since no natural PRV isolate has been reported to contain EcoRI sites, the isolation and single-step growth curve analysis of these mutants established that PRV can carry such a site with little ill effect in tissue culture. Virus carrying these defined mutations produced novel gIII proteins that enabled us to begin functional assignment of protein localization information within the gIII gene. Specifically, one viral mutant contained an in-frame synthetic EcoRI linker sequence that was flanked on one side by the first one-third of the gIII gene and on the other side by the last one-third of the gene. The resulting protein lacked the middle one-third of the parental species, including five of eight putative N-linked glycosylation signals, but was still glycosylated and found in enveloped virions; it was not secreted into the medium. A second viral mutant contained an in-frame synthetic EcoRI linker sequence that additionally specified a nonsense codon at position 158, producing a gIII protein that was glycosylated and secreted into the medium; the fragment was not found in enveloped virions. By endoglycosidase and pulse-chase analyses, we established a precursor-product relationship between the various forms of gIII expressed in the parental and mutant strains, and perhaps determined certain features of the gIII protein that are required for its efficient export within the cell.

The single base pair substitution responsible for the Syn phenotype of herpes simplex virus type 1, strain MP

Nucleotide sequences were determined for portions of the genomes of the syncytial (Syn) mutant of herpes simplex virus type 1, strain MP, and the related wild-type strain mP. Comparisons of the nucleotide sequences showed only 1 bp difference between the DNAs of strains MP and mP in the region to which the Syn mutation of MP had previously been mapped. This base pair substitution in MP (at map coordinate 0.737) eliminates a ThaI restriction endonuclease recognition site that is present in mP DNA. Analyses of MP X mP recombinant viruses showed that presence of the ThaI site correlates with the Syn+ phenotype and absence of the ThaI site correlates with the Syn phenotype as predicted. We conclude that the base pair substitution at map coordinate 0.737 is responsible for the Syn phenotype of MP. This mutation could alter translation in four of the six reading frames, causing amino acid substitutions. From only one of these reading frames is a product likely to be expressed. The 338-amino acid polypeptide that could be expressed has features characteristic of membrane-associated proteins, including hydrophobic domains, potential sites for the attachment of N-linked carbohydrate, and a potential cleavable signal sequence.

Transcriptional control signals of a herpes simplex virus type 1 late (gamma 2) gene lie within bases -34 to +124 relative to the 5' terminus of the mRNA

The cis-acting DNA sequences required for regulated expression of a herpes simplex virus type 1 (HSV-1) late (gamma 2) gene were studied by using viruses containing specific deletions in the 5' transcribed noncoding and upstream regions of the HSV-1 glycoprotein C (gC) gene, a model gamma 2 gene. Nine mutant viruses which had variable 5' and 3' deletions within bases -569 to +124 relative to the 5' terminus of the gC mRNA were isolated. The mutants were isolated by a simple in situ hybridization screening procedure not requiring any prior selective pressure for or against expression of the gC gene. Analysis of RNA extracted from cells infected with individual mutants showed that the DNA sequences required for regulated expression of this gamma 2 gene lay within bases -34 to +124. This 158-base-pair fragment was sufficient to confer accurate and quantitative expression of gC mRNA and to maintain the stringent requirement on viral DNA replication for expression of this gene. Moreover, it was found that sequences located between -34 and +14 contained signals essential for expression of gC. To determine whether the -34 to +124 sequences would function as a gamma 2 promoter when moved to another region of the HSV-1 genome, the 158-base-pair fragment was substituted for the normal thymidine kinase promoter-regulatory sequences in the thymidine-kinase gene locus. Transcription of this chimeric gene was regulated as a gamma 2 gene in that its expression in infected cells was dependent on viral DNA synthesis. The only recognizable consensus sequence upstream of the transcription initiation site for this gene was the TATAAA sequence at -30.

Expression of cell-associated and secreted forms of herpes simplex virus type 1 glycoprotein gB in mammalian cells

The gene for glycoprotein gB1 of herpes simplex virus type 1 strain Patton was expressed in stable Chinese hamster ovary cell lines. Expression vectors containing the dihydrofolate reductase (dhfr) cDNA plus the complete gB1 gene or a truncated gene lacking the 194 carboxyl-terminal amino acids of gB1 were transfected into CHO DHFR-deficient cells. Radioimmunoprecipitation demonstrated that the complete gB1 protein expressed in CHO cell lines was cell associated, whereas the truncated protein was secreted from the cells due to deletion of the transmembrane and C-terminal domains of gB1. Cells expressing the truncated gB1 protein were subjected to stepwise methotrexate selection, and a cell line was isolated in which the gB1 gene copy number had been amplified 10-fold and the level of expression of gB1 had increased over 60-fold. The truncated gB1 protein was purified from medium conditioned by the amplified cell line. N-terminal amino acid sequence analysis of this purified protein identified the signal peptide cleavage site and predicted the cleavage of a 30-amino-acid signal sequence from the primary protein. The immunogenicity of the truncated gB1 protein was also tested in mice, and high levels of antibody and protection from virus challenge were observed.

Physical mapping of two herpes simplex virus type 1 host shutoff loci: rescue of each ts mutation occurs with two unique cloned regions of the viral genome

Two complementing temperature-sensitive (ts) herpes simplex virus type 1 (HSV-1) mutants, PAA1rts1 and ts199, were defective in viral DNA synthesis and in the shutoff of cellular macromolecular synthesis at 39.5 degrees C, the nonpermissive temperature. PAA1sts1 and PAA1rts1+ recombinants and PAA1rts1+ revertants were used to examine the contributions of the PAA1r mutation and the ts1 mutation of PAA1rts1 in affecting the levels of viral and cellular DNA synthesized at 34 and 39.5 degrees C. The results of this study suggests an interaction between the viral DNA polymerase and the ts1+ gene product during HSV-1 DNA replication and possibly in the inhibition of host DNA synthesis by HSV-1. Physical mapping of the ts mutations present in ts199 and the PAA1sts1 recombinant ts1-8 were performed by intratypic marker rescue experiments. Surprisingly, both the ts1-8 and ts199 mutations were rescued by two cloned fragments: ts1-8 by BglII-K (map coordinates 0.095 to 0.163) and BglII-I (map coordinates 0.314 to 0.417), while ts199 was rescued by BglII-K and BglII-O (map coordinates 0.163 to 0.197). In more refined mapping experiments, the regions between coordinates 0.347 to 0.378 and 0.126 to 0.163 were able to rescue the ts1-8 mutation. Southern hybridization analysis confirmed that the fragments that rescued ts1-8 and those that rescued ts199 had homology, as predicted by the physical mapping results.

The nucleotide sequence of the gB glycoprotein gene of HSV-2 and comparison with the corresponding gene of HSV-1

The nucleotide sequence of the gB glycoprotein gene of HSV-2 has been determined and compared with the homologous gene of HSV-1. The two genes are specified by the same total number of codons (904); eight additional codons of the HSV-1 gene are found within the signal sequence, and eight additional codons of the HSV-2 gene are found at three different sites in the gene. The signal cleavage, membrane-spanning, and eight potential N-linked oligosaccharide sites, as well as 5'- and 3'-regulatory signals are largely conserved. The overall amino acid homology is 85%; least conserved are the N- and C-terminal regions of the protein. Secondary structure plots were determined for the two proteins, and the structures were compared with each other and with alterations in structure due to several mutations in the HSV-1 gB gene for which sequence analysis is available. The high homology in primary and secondary structure suggests a conserved, essential function for the gene.

Map location of the gene for a 130,000-dalton glycoprotein of bovine herpesvirus 1

A bovine herpesvirus 1 variant (mar6) containing a mutation in a viral glycoprotein with a molecular weight of 130,000 (g130) was isolated by selecting for resistance to a neutralizing monoclonal antibody (130-6) directed against g130. Mar6 was completely resistant to neutralization by monoclonal antibody 130-6 in the presence and absence of complement, but was neutralized by polyvalent immune sera. The mar6 mutant synthesized and processed g130, but produced plaques which failed to react with monoclonal antibody 130-6 in an in situ immunoassay (black plaque). However, monoclonal antibody 130-6 was capable of binding and immunoprecipitating g130 from infected-cell extracts produced by lysis of mar6-infected cells with nonionic detergents. The mutation in mar6 was mapped by marker rescue with cloned bovine herpesvirus 1 restriction enzyme fragments to a 3.8-kilobase fragment at approximate map units 0.405 to 0.432. In addition, it was found that a DNA probe containing the glycoprotein B gene of herpes simplex type 1 hybridized uniquely to the same 3.8-kilobase fragment which was shown by marker rescue to contain the mutation site in the gene for bovine herpesvirus 1 g130.

Transcriptional control signals of a herpes simplex virus type 1 late (gamma 2) gene lie within bases -34 to +124 relative to the 5' terminus of the mRNA

The cis-acting DNA sequences required for regulated expression of a herpes simplex virus type 1 (HSV-1) late (gamma 2) gene were studied by using viruses containing specific deletions in the 5' transcribed noncoding and upstream regions of the HSV-1 glycoprotein C (gC) gene, a model gamma 2 gene. Nine mutant viruses which had variable 5' and 3' deletions within bases -569 to +124 relative to the 5' terminus of the gC mRNA were isolated. The mutants were isolated by a simple in situ hybridization screening procedure not requiring any prior selective pressure for or against expression of the gC gene. Analysis of RNA extracted from cells infected with individual mutants showed that the DNA sequences required for regulated expression of this gamma 2 gene lay within bases -34 to +124. This 158-base-pair fragment was sufficient to confer accurate and quantitative expression of gC mRNA and to maintain the stringent requirement on viral DNA replication for expression of this gene. Moreover, it was found that sequences located between -34 and +14 contained signals essential for expression of gC. To determine whether the -34 to +124 sequences would function as a gamma 2 promoter when moved to another region of the HSV-1 genome, the 158-base-pair fragment was substituted for the normal thymidine kinase promoter-regulatory sequences in the thymidine-kinase gene locus. Transcription of this chimeric gene was regulated as a gamma 2 gene in that its expression in infected cells was dependent on viral DNA synthesis. The only recognizable consensus sequence upstream of the transcription initiation site for this gene was the TATAAA sequence at -30.

Role of glycoproteins of pseudorabies virus in eliciting neutralizing antibodies

The experiments described in this paper were designed to assess the role of the various virus glycoproteins of pseudorabies virus (PrV) in eliciting the production of neutralizing antibodies during the normal course of infection of swine. They also address the question of the degree of antigenic variation within each glycoprotein between different virus isolates. The results show the following: Antigenic variation between strains of PrV isolated from different geographic areas are readily detectable; antigenic differences between strains isolated from the same geographic area are less common. No antigenic drift in glycoprotein gII was observed. Glycoprotein gIII and, to some extent, also glycoprotein gI showed a high level of antigenic drift. The neutralizing activity of pooled convalescent sera of swine is not directed against glycoprotein gI. A large part of the neutralizing activity of pooled convalescent sera of swine is directed against glycoprotein gIII.

Pseudorabies virus gene encoding glycoprotein gIII is not essential for growth in tissue culture

We have established that in the Becker strain of pseudorabies virus (PRV), the glycoprotein gIII gene is not essential for growth in cell culture. This was accomplished by construction and analysis of viral mutants containing two defined deletion mutations affecting the gIII gene. These mutations were first constructed in vitro and introduced into Escherichia coli expression plasmids to verify structure and protein production. Each mutation was then crossed onto PRV by cotransfection of plasmid DNA and parental viral DNA by using gIII-specific monoclonal antibodies as selective and screening reagents. One resultant virus strain, PRV-2, contained an in-frame deletion of a 402-base-pair (bp) SacI fragment contained within the gIII gene. Another virus strain, PRV-10, contained a deletion of a 1,480-bp XhoI fragment removing 230 bp of the upstream, putative transcriptional control sequences and 87% of the gIII coding sequence. The deletion mutants were compared with parental virus by analysis of virion DNA, gIII specific RNA, and proteins reacting with gIII specific antibodies. Upon infection of PK15 cells, the deletion mutants did not produce any proteins that reacted with two gIII specific monoclonal antibodies. However, two species of truncated glycosylated proteins were observed in PRV-2 infected cells that reacted with antiserum raised against bacterially produced gIII protein. PRV-10 produced no detectable gIII-specific RNA or protein. PRV-10 could be propagated without difficulty in tissue culture. Virus particles lacking gIII were indistinguishable from parental PRV virus particles by analysis of infected-cell thin sections in the electron microscope. We therefore conclude that expression of the gIII gene was not absolutely essential for PRV growth in tissue culture.

Antigenic variation (mar mutations) in herpes simplex virus glycoprotein B can induce temperature-dependent alterations in gB processing and virus production

Monoclonal antibody-resistant (mar) mutants altered in the antigenic structure of glycoprotein B (gB) of herpes simplex virus type 1, strain KOS-321, were selected by neutralization with each of six independently derived gB-specific monoclonal antibodies. Analysis of the reactivity patterns of these mar mutants with a panel of 16 virus-neutralizing monoclonal antibodies identified at least five nonoverlapping epitopes on this antigen, designated groups I through V. Multiple mar mutations were also introduced into the gB structural gene by recombination and sequential antibody selection to produce a set of mar mutants with double, triple, and quadruple epitope alterations. Group II (B2) and group III (B4) antibodies were used to select the corresponding mutants, mar B2.1 and mar B4.1, which in addition to carrying the mar phenotype were temperature sensitive (ts) for processing of the major partially glycosylated precursor of gB, pgB (Mr = 107,000), to mature gB (Mr = 126,000) and showed reduced levels of gB on the cell surface at high temperature (39 degrees C). These mutants were not, however, ts for production of infectious progeny. A recombinant virus, mar B2/4.1, carrying both of these alterations was ts for virus production and failed to produce and transport any detectable mature gB to the cell surface at 39 degrees C. Rather, pgB accumulated in the infected cell. Revertants of the ts phenotype, isolated from virus plaques at 39 degrees C, regained the B2 but not the B4 epitope and were phenotypically indistinguishable from the mar B4.1 parent. Finally, it was shown that group II (B5) and group III (B4) antibodies failed to immunoprecipitate pgB (39 degrees C) produced by ts gB mutants of herpes simplex virus type 1 which were not selected with monoclonal antibodies. Taken together, our findings indicate that (i) mar mutations can alter antigenic as well as other functional domains of gB, namely, the domain(s) involved in processing and infectivity, and (ii) group II and group III epitopes lie within an essential functional domain of gB which is a target for ts gB mutations.

Molecular basis of the glycoprotein C-negative phenotypes of herpes simplex virus type 1 mutants selected with a virus-neutralizing monoclonal antibody

Previously (Holland et al., J. Virol. 52:566-574, 1984; Kikuchi et al., J. Virol. 52:806-815, 1984) we described the isolation and partial characterization of over 100 herpes simplex virus type 1 mutants which were resistant to neutralization by a pool of glycoprotein C- (gC) specific monoclonal antibodies. The genetic basis for the inability of several of these gC- mutants to express an immunoreactive envelope form of gC is reported here. Comparative nucleotide sequence analysis of the gC gene of the six mutants gC-3, gC-8, gC-49, gC-53, gC-85, and synLD70, which secrete truncated gC polypeptides, with that of the wild-type KOS 321 gC gene revealed that these mutant phenotypes were caused by frameshift or nonsense mutations, resulting in premature termination of gC translation. Secretion of the gC polypeptide from cells infected with these mutants was due to the lack of a functional transmembrane anchor sequence. The six secretor mutants were tested for suppression of amber mutations in mixed infection with a simian virus 40 amber suppressor vector. Mutant gC-85 was suppressed and produced a wild-type-sized membrane-bound gC. Nucleotide sequence analysis of the six gC deletion mutants gC-5, gC-13, gC-21, gC-39, gC-46, and gC-98 revealed that they carried identical deletions which removed 1,702 base pairs of the gC gene. The deletion, which was internal to the gC gene, removed the entire gC coding sequence and accounted for the novel 1.1-kilobase mRNA previously seen in infections with these mutants. The mutant gC-44 was previously shown to produce a membrane-bound gC protein indistinguishable in molecular weight from wild-type gC. This mutant differed from wild-type virus in that it had reduced reactivity with virus-neutralizing monoclonal antibodies. Nucleotide sequence analysis of the gC gene of mutant gC-44 demonstrated a point mutation which changed amino acid 329 of gC from a serine to a phenylalanine.

Expression and regulation of glycoprotein C gene of herpes simplex virus 1 resident in a clonal L-cell line

Ltk- cells were transfected with a plasmid containing the entire domain of glycoprotein C (gC), a true gamma or gamma 2 gene of herpes simplex virus 1 (HSV-1) and the methotrexate-resistant mouse dihydrofolate reductase mutant gene. The resulting methotrexate-resistant cell line was cloned; of the 39 clonal lines tested only 1, L3153(28), expressed gC after infection with HSV-1(MP), a gC- mutant, and none expressed gC constitutively. The induction of gC was optimal at multiplicities ranging between 0.5 and 2 PFU per cell, and the quantities produced were equivalent to or higher than those made by methotrexate-resistant gC- L cells infected with wild-type (gC+) virus. The gC gene resident in the L3153(28) cells was regulated as a beta gene inasmuch as the amounts of gC made in infected L3153(28) cells exposed to concentrations of phosphonoacetate that inhibited viral DNA synthesis were higher than those made in the absence of the drug, gC was induced at both permissive and nonpermissive temperatures by the DNA- mutant tsHA1 carrying a lesion in the gene specifying the major DNA-binding protein and which does not express gamma 2 genes at the nonpermissive temperature, and gC was induced only at the permissive temperature in cells infected with ts502 containing a mutation in the alpha 4 gene. The gC induced in L3153(28) cells was made earlier and processed faster to the mature form than that induced in a gC- clone of methotrexate-resistant cells infected with wild-type virus. Unlike virus stocks made in gC- cells, HSV-1(MP) made in L3153(28) cells was susceptible to neutralization by anti-gC monoclonal antibody.

Multiple adjacent or overlapping loci affecting the level of gC and cell fusion mapped by intratypic recombinants of HSV-1

We have prepared and analyzed 40 HSV-1 intratypic recombinants with regard to plaque morphology and glycoprotein C(gC) phenotypes. Vero cells have been cotransfected with the intact genome of HSV-1(F) and cloned or uncloned DNA fragments from HSV-1(MP) and recombinants inducing the fusion of Vero cells [syncytial (Syn) recombinants] have been selected and purified. Marker transfer of the Syn phenotype has been observed with the cloned BamHI L and B fragments (0.706-0.745 and 0.745-0.810 map units, respectively) as well as with the uncloned HpaI TXO fragment (0.710-0.761) from MP DNA. No marker transfer has been observed with F DNA alone or with the cloned BamHI N fragment (0.863-0.898 map units). When viruses expressing the Syn phenotype in Vero cells were tested in HEp-2 cells, three kinds of recombinants were observed. Members of the first class expressed a wild type, cytoaggregating (Syn+), plaque morphology in these cells. Members of the second class induced the complete fusion (Syn phenotype) of the cells. Members of the third class induced an intermediate plaque morphology, characterized by the formation of groups of polykaryocytes (fused cells) but without formation of a complete syncytium. All recombinants expressing the Syn+ phenotype in HEp-2 cells were also gC+, whereas recombinants expressing the Syn phenotype in these cells were gC- with one exception, in which low levels of gC could be detected (but clearly less than with HSV-1(F]. Concerning polykaryocytic class of recombinants, some of them were gC+ while others expressed only low amounts of gC; no gC- virus was observed within this class of recombinants. The three classes of recombinants were observed with each of the cloned BamHI L and B fragments and also with the HpaI TXO fragment, suggesting the existence of multiple adjacent or overlapping loci affecting plaque morphology and the control of the accumulation or the synthesis of gC at both sides of 0.745 map units.

Characterization and mapping of a nonessential pseudorabies virus glycoprotein

Antigenic variants of pseudorabies virus (PRV) containing mutations in a viral glycoprotein with a molecular weight of 82,000 (gIII) were isolated by selecting for resistance to a complement-dependent neutralizing monoclonal antibody (MCA82-2) directed against gIII. These mutants were completely resistant to neutralization with MCA82-2 in the presence of complement. Two mutants selected for further studies either did not express gIII or expressed an improperly processed form of the glycoprotein. The mutations were also associated with an altered plaque morphology (syncytium formation). The gIII gene was mapped by marker rescue of a gIII- mutant with cloned restriction enzyme fragments to the long unique region of the PRV genome between 0.376 and 0.383 map units. This corresponds to the map location of a glycoprotein described by Robbins et al. (J. Mol. Appl. Gen. 2:485-496, 1984). Since gIII is nonessential for viral replication in cell culture and has several other characteristics in common with the herpes simplex virus glycoprotein gC, gIII may represent the PRV equivalent to herpes simplex virus gC.

Pathogenicity in mice of herpes simplex virus type 2 mutants unable to express glycoprotein C

Herpes simplex virus type 2 (HSV-2) mutants that were unable to express glycoprotein C (gC-2) were isolated. Deletions were made in a cloned copy of the gC-2 gene, and recombinant viruses containing these deletions were screened by using an immunoreactive plaque selection protocol. The viruses did not display a syncytial phenotype. Intravaginal inoculation of BALB/cJ mice with one of the HSV-2 gC-2- viruses produced local inflammation followed by a lethal spread of the viral infection into the nervous system in a manner identical to that produced by parental HSV-2 strain 333. Similarly, intracerebral inoculation of DBA-2 mice with the gC-2- virus produced a lethal neurological disease paralleling that caused by HSV-2 strain 333. These results indicate that gC-2 is not required for the spread of HSV-2 infections in mice.

Construction of an infectious pseudorabies virus recombinant expressing a glycoprotein gIII-beta-galactosidase fusion protein

An infectious herpesvirus mutant has been constructed in which a major structural envelope glycoprotein gene was replaced by a hybrid gene encoding a novel fusion protein consisting of the N-terminus of the viral glycoprotein joined to Escherichia coli beta-galactosidase (beta Gal). Specifically, we fused DNA encoding the first 157 amino acids of the structural glycoprotein gIII from pseudorabies virus strain Becker to the E. coli lacZ gene in a bacterial expression vector. The resulting hybrid gene was then used to replace the wild-type gIII gene in the virus by cotransfection of plasmid and viral DNA. The desired viral recombinants were identified by their inability to react with specific monoclonal antibodies that recognized only wild-type gIII protein. One such mutant virus, PRV-Z1, was chosen for further analysis. PRV-Z1 expressed a glycosylated gIII-beta Gal fusion protein after infection of PK15 cells. The fusion protein has no demonstrable beta Gal activity and, although glycosylated, remains sensitive to the enzyme endo-beta-N-acetylglucosaminidase H, unlike the mature gIII gene product, indicating that the fusion protein was incompletely processed.

Passive immune protection by herpes simplex virus-specific monoclonal antibodies and monoclonal antibody-resistant mutants altered in pathogenicity

Virus-neutralizing monoclonal antibodies specific for 13 different genetically defined epitopes of glycoproteins gC, gB, and gD of herpes simplex virus type 1, strain KOS-321, were compared for their ability to provide passive immunity to DBA-2 mice challenged intracranially. Protection was highly specific, since individual monoclonal antibodies failed to protect against infection with monoclonal antibody-resistant (mar) mutants altered in the single epitope recognized by the injected antibody. The dose-response kinetics of passive immunity paralleled the in vitro neutralization titers for each antibody. No correlation was observed between immune protection and antibody isotype or complement-dependent in vitro neutralization titers. This suggests that virus neutralization was not the protective mechanism. In general, antibodies reactive with epitopes of gC were protective at the lowest antibody doses, antibodies specific for gB were less efficient in providing immunity, and antibodies against gD were the least effective. mar mutants with single epitope changes in gC and multiple epitope changes in gB showed highly reduced pathogenicity, requiring up to 5 X 10(6) PFU to kill 50% of infected animals. These findings indicated that antigenic variation affects virus growth and spread in the central nervous system. Thus, mutations which affect antigenic structure also can alter virus pathogenicity. The alteration of these epitopes does not, however, appreciably reduce the development of resistance to infection. Infection of mice with these mutants or inoculation of mice with UV-inactivated, mutant-infected cells before challenge rendered the animals resistant to infection with wild-type herpes simplex virus type 1.

Pseudorabies virus avirulent strains fail to express a major glycoprotein

The unique short (Us) region of the pseudorabies virus (PRV) genome, which displays high transcriptional activity during the late phase of infection and has been found to code for glycoproteins, is partially deleted in the genomes of three vaccine strains (A57, Norden, and NIA-4). This deletion is located in the SalI subfragment 7A of BamHI fragment 7. To identify possible viral gene products involved in PRV virulence, we investigated the transcriptional and translational pattern of the deleted part of the Us region. Northern blots demonstrated that one major RNA species (3.8 kilobases) transcribed from fragment 7A was missing in the vaccine strains, whereas other transcripts were altered. Radioimmunoprecipitation of in vivo-labeled PRV glycoproteins and of in vitro-translated polypeptides with hyperimmune serum and monoclonal antibodies indicated a lack of glycoprotein gI. Hybrid-selection experiments with subcloned DNA fragments confirmed the absence of gI and of a 40,000-molecular-weight polypeptide. We suggest that both viral proteins are involved in the expression of PRV virulence.

Anatomy of the herpes simplex virus 1 strain F glycoprotein B gene: primary sequence and predicted protein structure of the wild type and of monoclonal antibody-resistant mutants

In this paper we report the nucleotide sequence and predicted amino acid sequence of glycoprotein B of herpes simplex virus 1 strain F and the amino acid substitutions in the domains of the glycoprotein B gene of three mutants selected for resistance to monoclonal antibody H126-5 or H233 but not to both. Analyses of the amino acid sequence with respect to hydropathicity and secondary structure yielded a two-dimensional model of the protein. The model predicts an N-terminal, 29-amino-acid cleavable signal sequence, a 696-amino-acid hydrophilic surface domain containing six potential sites for N-linked glycosylation, a 69-amino-acid hydrophobic domain containing three segments traversing the membrane, and a charged 109-amino-acid domain projecting into the cytoplasm and previously shown to marker rescue glycoprotein B syn mutations. The nucleotide sequence of the mutant glycoprotein B DNA fragments previously shown to marker transfer or rescue the mutations revealed that the amino acid substitutions cluster in the hydrophilic surface domain between amino acids 273 and 305. Analyses of the secondary structure of these regions, coupled with the experimentally derived observation that the H126-5- and H233-antibody cognitive sites do not overlap, indicate the approximate locations of the epitopes of these neutralizing, surface-reacting, and immune-precipitating monoclonal antibodies. The predicted perturbations in the secondary structure introduced by the amino acid substitutions correlate with the extent of loss of reactivity with monoclonal antibodies in various immunoassays.

Herpes simplex virus type 1 glycoprotein C-negative mutants exhibit multiple phenotypes, including secretion of truncated glycoproteins

A virus-neutralizing monoclonal antibody specific for glycoprotein C (gC) of herpes simplex virus type 1 strain KOS was used to select a number of neutralization-resistant mutants. A total of 103 of these mutants also were resistant to neutralization by a pool of gC-specific antibodies and thus were operationally defined as gC-. Analysis of mutant-infected cell mRNA showed that a 2.7-kilobase mRNA, comparable in size to the wild-type gC mRNA, was produced by nearly all mutants. However, six mutants, gC-5, gC-13, gC-21, gC-39, gC-46, and gC-98, did not produce the normal-size gC mRNA but rather synthesized a novel 1.1-kilobase RNA species. These mutants had deletions of 1.6 kilobases in the coding sequence of the gC structural gene, which explains their gC- phenotype. Despite the production of an apparently normal mRNA by the remaining 97 mutants, only 7 mutants produced a detectable gC polypeptide. In contrast to wild-type gC, which is a membrane-bound glycoprotein with an apparent molecular weight of 130,000 (130K), five of these mutants quantitatively secreted proteins of lower molecular weight into the culture medium. These were synLD70 (101K), gC-8 (109K), gC-49 (112K), gC-53 (108K), and gC-85 (106K). The mutant gC-3 secreted a protein that was indistinguishable in molecular weight from wild-type KOS gC. Another mutant, gC-44, produced a gC protein which also was indistinguishable from wild-type gC by molecular weight and which remained cell associated. Pulse-labeling of infected cells in the presence and absence of the glycosylation inhibitor tunicamycin demonstrated that these proteins were glycosylated and provided estimates of the molecular weights of the nonglycosylated primary translation products. The smallest of these proteins was produced by synLD70 and was 48K, about two-thirds the size of the wild-type polypeptide precursor (73K). Physical mapping of the mutations in synLD70 and gC-8 by marker rescue placed these mutations in the middle third of the gC coding sequence. Mapping of the mutations in other gC- mutants, including two in which no protein product was detected, also placed these mutations within or very close to the gC gene. The biochemical and genetic data available on mutants secreting gC gene products suggest that secretion is due to the lack of a functional transmembrane anchor sequence on these mutant glycoproteins.

Characterisation of a herpes simplex virus type 1 mutant which has a temperature-sensitive defect in penetration of cells and assembly of capsids

A herpes simplex virus type 1 (HSV-1) mutant, ts1204, which has a temperature-sensitive (ts) mutation located within genome map coordinates 0.318 to 0.324, close to but outside the coding sequences of the glycoprotein gB gene, has been characterised. Although this mutant adsorbed to the cell surface at the nonpermissive temperature (NPT), it failed to penetrate the cell membrane. As a consequence of this defect, high multiplicities of infection of ts1204 blocked subsequent infection of cells by wild-type HSV-1. By contrast, at the NPT, superinfection of cells with HSV-2 was not inhibited by prior infection with ts1204. The penetration defect could be overcome either by brief incubation of mutant virus-infected cells at the permissive temperature, or by treatment of the cells with polyethylene glycol, a compound which promotes fusion of membranes. Upon continued incubation of ts1204-infected cells at the NPT, low numbers of capsids were assembled. Although these capsids all had some internal structure, they did not contain DNA. Another mutant, ts1208, which lies in the same complementation group as ts1204, penetrated cells normally at the NPT, but like ts1204, had a defect in the formation of functional capsids. Evidence presented in this paper suggests that the gene in which the ts1204 and ts1208 lesions map encodes a structural polypeptide.

Binding to cells of virosomes containing herpes simplex virus type 1 glycoproteins and evidence for fusion

Envelope proteins and lipids were extracted from purified herpes simplex virus type 1 virions with octyl glucoside and mixed with phosphatidylcholine for preparation of virosomes by removal of the detergent. Greater than 85% of the extracted envelope proteins, including all the glycoproteins and the nonglycosylated protein designated VP16, were associated with virosomes, which ranged in density from ca. 1.07 to 1.13 g/cm3. All the glycoproteins except gC were as susceptible to degradation by added protease in virosomes as in virions, indicating similar orientations in both. Approximately 30 to 40% of radiolabel incorporated into virosomes bound to HEp-2 cells within 1.5 h at either 4 or 37 degrees C. The cell-bound virosomes were enriched for gB and deficient in other glycoproteins, in comparison with unbound or total virosomes. Binding of virosomes to HEp-2 cells could be inhibited by purified virus, heparin, and monospecific antiviral antibodies. Polyclonal and monoclonal anti-gB antibodies were more effective at inhibiting virosome binding than were anti-gD or anti-gC antibodies. Virosomes depleted of gB or gD did not bind to cells as efficiently as did virosomes containing all the extracted enveloped components; this loss of binding activity was especially pronounced on depletion of gB. The binding of herpes simplex virus type 1 virosomes to cells is discussed in relation to possible heterogeneity of the virosomes and comparisons with binding of virions to cells. We also present electron microscopic evidence that bound virosomes can fuse with the cell surface.

Genome locations of temperature-sensitive mutants in glycoprotein gB of herpes simplex virus type 1

A plasmid containing a herpes simplex virus type 1 (HSV-1) insert from strain KOS, prototypic coordinates 0.345 to 0.368 (3.45 kilobases) was mutagenized in vitro, and potential mutations were introduced into intact viral DNA by cotransfection. Functions normally associated with the glycoprotein gB are in the 1-9 complementation group, and the above coordinates include those that specify the gB glycoprotein gene. Following cotransfection, individual plaques were screened for temperature sensitivity (ts) of viral growth. A total of seven ts mutants was obtained, of which four were spurious mutations due to alterations outside the cloned sequences, presumably mediated by some aspect of the Ca-precipitation-cotransfection method. The remaining three did not complement known mutants of the 1-9 complementation group. These three mutants, along with tsJ12 (P.A. Schaffer, G.M. Aron, N. Biswal, and M. Benyesh-Melnick, 1973, Virology 52, 57-71) and tsJ33 (C.-T. Chu, D.S. Parris, R.A.F. Dixon, F.E. Farber, and P.A. Schaffer, 1979, Virology 98, 168-181), were physically located by marker-rescue experiments to three different restriction fragments between 0.345 to 0.368 map units. Sodium dodecyl sulfate-gel electrophoresis was used to analyze the glycoproteins synthesized during continuous or pulse-chase labeling protocols. All five mutants were found to synthesize a precursor of gB but did not accumulate mature gB during a pulse, a chase, or continuous labeling at the nonpermissive temperature.

Nucleotide sequence of a region of the herpes simplex virus type 1 gB glycoprotein gene: mutations affecting rate of virus entry and cell fusion

The tsB5 isolate of herpes simplex virus type I (HSV-1) enters host cells more rapidly than does KOS, an independent isolate of HSV-1, and this rate-of-entry determinant is located between prototypic map coordinates 0.350 and 0.360 (1). The nucleotide sequence of strain tsB5 has now been determined between prototypic map coordinates 0.347 and 0.360. Comparison of the tsB5 sequence to the homologous KOS sequence revealed that the rate-of-entry difference between these two HSV-1 strains may be due to the single amino acid difference observed within these sequences (0.350 to 0.360). A cell fusion determinant in tsB5 is located between coordinates 0.345 and 0.355 and to the left of the rate-of-entry determinant (1). Nucleotide sequence analysis revealed a second amino acid difference between tsB5 and KOS at coordinate 0.349. The cell fusion determinant was tentatively assigned to this location.

Fine mapping of mutations in the fusion-inducing MP strain of herpes simplex virus type 1

Previous studies [W. T. Ruyechan, L. S. Morse, D. M. Knipe, and B. Roizman (1979) J. Virol. 29, 677-697] have shown that multiple mutations are responsible for the mutant phenotypes of herpes simplex virus type 1, strain MP, and have indicated that these mutations may be located on the genome between map coordinates 0.70 and 0.83. Strain MP produces large syncytial (Syn) plaques on many cell types and does not express glycoprotein C (gC-), whereas a sibling strain mP produces wild-type, small, nonsyncytial (Syn+) plaques and is gC+. Cloned DNA fragments from strains MP and mP (and strain F) were used in marker transfer and marker rescue experiments to map more precisely the mutations in MP. It was found that a 680-bp fragment from MP DNA (map coordinates 0.735 to 0.740) could transfer a Syn marker to mP and that, conversely, an overlapping fragment from mP DNA (map coordinates 0.728 to 0.744) could rescue the Syn mutation of MP. Recombinant viruses obtained in these experiments differed from the donor of the cloned DNA fragment in plaque size, however, indicating that mutation(s) at other regions of the MP genome cause enlarged plaques, in which the infected cells are less rounded than in wild-type plaques. A fragment of MP DNA from map coordinates 0.60 to 0.64 transferred a mutation causing the gC- phenotype to strain mP, and a fragment of F DNA from map coordinates 0.62 to 0.64 rescued the gC- mutation of MP. These results, coupled with data published by Frink et al. [(1983) J. Virol. 45, 643-467], indicate that the mutation responsible for the gC- phenotype of MP may be in the structural gene for gC.

Isolation, characterization, and physical mapping of a pseudorabies virus mutant containing antigenically altered gp50

A pseudorabies virus variant ( mar197 -1) containing a mutation in a viral glycoprotein with a molecular weight of 50,000 ( gp50 ) was isolated by selecting for resistance to a neurtralizing monoclonal antibody ( MCA50 -1) directed against gp50 . This mutant was completely resistant to neutralization with MCA50 -1 in the presence or absence of complement, and was therefore defined as a mar (monoclonal-antibody-resistant) mutant. The mutation did not affect neutralization with polyvalent immune serum. The mar197 -1 mutant synthesized and processed gp50 normally, but the mutation prevented the binding and immunoprecipitation of gp50 by MCA50 -1. Thus, the mutation was within the structural portion of the gp50 gene affecting the epitope of the monoclonal antibody. The mutation was mapped by marker rescue with cloned pseudorabies restriction enzyme fragments to the short region of the pseudorabies genome between 0.813 and 0.832 map units. This is equivalent to a 2.1-kilobase-pair region.

Mutations affecting conformation or sequence of neutralizing epitopes identified by reactivity of viable plaques segregate from syn and ts domains of HSV-1(F) gB gene

Three classes of HSV-1(F) mutants expressing a resistance phenotype to two highly potent-type common monoclonal antibodies, H126-5 and H233, to glycoprotein B (gB) were selected. Class 1 mutants, selected for resistance to neutralization from nonmutagenized virus stocks, expressed a gB which reacted in biotin-avidin-enhanced surface immunoassays and in immune precipitation tests with the selecting antibodies. Class 2 and 3 mutants were selected for nonreactivity in the biotin-avidin-enhanced surface immunoassay from BUdR-mutagenized, preneutralized virus stocks, but differ in that the selecting antibodies immune precipitated the gB of Class 2 but not that of Class 3. Mutants expressing a resistance phenotype to one monoclonal antibody (H126-5 or H233) invariably retained reactivity in all tests with the heterologous antibody, and recombinants resistant to both antibodies were produced by cotransfection of intact DNA of one mutant with a cloned DNA fragment from another mutant. Class 1 mutations were mapped by marker transfer to a 1734-bp DNA fragment. Class 2 and 3 mutations were mapped to a region defined by a maximum of 377 bp and a minimum of 46 bp, in a biotin-avidin-enhanced surface immunoassay with a panel of DNA fragments of HSV-1(F) BamHI G carrying staggered deletions across the region encoding gB. This region does not overlap the neutralizing antibody determinant site mapped by T.C. Holland, R.M. Sandri-Goldin, L.E. Holland, S.D. Marlin, M. Levine, and J. Glorioso (1983, J. Virol. 46, 649-652) and is located 3' to the ts lesion of HSV-1(HFEM)tsB5 and 5' to the syn3 locus of that virus. It was concluded that (i) inasmuch as the biotin-avidin-enhanced surface immunoassay does not destroy the virus contained in the plaque, it is a rapid and convenient method for both identification and selection of mutants reactive and nonreactive to specific monoclonal antibodies. (ii) gB may contain multiple domains carrying epitopic sites of neutralizing monoclonal antibodies. (iii) The resistance phenotype may arise from mutations which alter the conformation or the amino acid sequence of the epitope. These mutations might be differentiable on the basis of reactivity of mutated gB with selecting monoclonal antibody in nondenaturing and denaturing environments, respectively.

Nucleotide sequence specifying the glycoprotein gene, gB, of herpes simplex virus type 1

The nucleotide sequence thought to specify the glycoprotein gene, gB, of the KOS strain of herpes simplex virus type 1 (HSV-1) has been determined. A 3.1-kilobase (kb), viral-specified RNA was mapped to the left half of the BamHI-G fragment (0.345 to 0.399 map units). TATA, CAT-box, and possible mRNA start sequences characteristic of HSV-1 genes are found near 0.368 map units. The first available ATG codon is at 0.366 and the first in-phase chain terminator at 0.348 map units. A polyA-addition signal (AATAAA) occurs 17 nucleotides past the chain terminator. Translation of these sequences would yield a 100.3-kilodalton (kDa) polypeptide characterized by a 5' signal sequence, nine N-linked saccharide addition sites, a strongly hydrophobic membrane-spanning sequence, and a highly charged 3' cytoplasmic anchor sequence. Two mutants of KOS, tsJ12 and tsJ20, that are temperature-sensitive for viral growth and for the production of gB, have been physically mapped to 0.357 to 0.360 and 0.360 to 0.364 map units, respectively (DeLuca et al., in preparation). The nucleotide sequence of the mutants was determined in these regions. In both cases a single amino acid replacement within the 100.3-kDa polypeptide is predicted from the sequence analysis.

Characterization of the major mRNAs transcribed from the genes for glycoprotein B and DNA-binding protein ICP8 of herpes simplex virus type 1

The structural genes encoding the herpes simplex virus type 1 glycoprotein B and the major DNA-binding protein ICP8 have been mapped previously within the EcoRI-F restriction fragment (map coordinates 0.314 to 0.420) of the viral genome. In this study the mRNAs transcribed from these DNA sequences were identified by hybridization selection of 32P-labeled RNA and by Northern blot analysis of polyadenylated cytoplasmic RNA. A 3.4-kilobase RNA was the major mRNA homologous to the DNA sequences between coordinates 0.343 and 0.386 in which mutations in the glycoprotein B gene have been mapped. A 4.5-kilobase RNA was the major mRNA homologous to the viral DNA sequences between coordinates 0.361 and 0.417 in which mutations in the ICP8 gene have been mapped. Hybridization-selected mRNAs were translated in vitro to determine the primary translation products encoded in each region. The glycoprotein B- and ICP8-specific polypeptides were identified by immunoprecipitation with specific antisera. The translation products encoded by the glycoprotein B gene were 103,000 and 99,000 in molecular weight. The translation products encoded by the ICP8 gene were 125,000 and 122,000 in molecular weight.

Transcriptional and genetic analyses of the herpes simplex virus type 1 genome: coordinates 0.29 to 0.45

We have constructed a map of the genes encoded by a 23,000-nucleotide-pair region of herpes simplex virus type 1. This region, defined by the three adjacent EcoRI fragments N (map coordinates 0.298 to 0.315), F (0.315 to 0.421), and M (0.421 to 0.448), has previously been shown by genetic analysis to contain the genes for thymidine kinase, nucleocapsid protein p40, glycoprotein B, DNA-binding protein, and DNA polymerase. We report the identification and mapping of RNAs defining 13 viral genes encoded by the region 0.298 to 0.448. The transcriptional pattern shows families of overlapping messages, similar to those observed in other regions of the viral genome. We also isolated mutants representing four distinct complementation groups and physically mapped several of the mutations to regions within EcoRI fragment F by marker rescue. Mutations representing complementation groups 1-9 (glycoprotein B), 1-1 (DNA-binding protein), and 1-3 (DNA polymerase) were mapped to coordinates 0.361 to 0.368 to 0.411, and 0.411 to 0.421, respectively. A fourth previously undefined complementation group was mapped to the region between glycoprotein B and DNA-binding protein. Comparing the transcription mapping with marker rescue data suggests that the genes for glycoprotein B, DNA-binding protein, DNA polymerase, and nucleocapsid protein p40 are expressed as 3.3-, 4.2-, 4.3- or 4.2- or both, and 2.4-kilobase mRNAs, respectively.

Expression of herpes simplex virus beta and gamma genes integrated in mammalian cells and their induction by an alpha gene product

The proteins of herpes simplex virus type 1 (HSV-1) form three kinetic groups termed alpha, beta, and gamma, whose synthesis is regulated in a cascade fashion. alpha products are synthesized first during infection, and they are required for synthesis of beta and gamma proteins. To examine the expression of several HSV-1 beta and gamma genes in the absence of alpha functions, we transferred into mammalian cells a plasmid containing a region of the HSV-1 genome that codes for only beta and gamma genes (0.315 to 0.421 map units). We found stable integration of at least one copy of the intact plasmid in each cell line. Four HSV-1 transcripts of the beta and gamma classes were transcribed constitutively in the cells, including the genes for glycoprotein B and DNA-binding protein. No constitutive synthesis of these two proteins could be demonstrated, however. The integrated HSV-1 genes responded to viral regulatory signals in that they could be induced by infection with HSV-1 mutants resulting in a high level of synthesis of both glycoprotein B and DNA-binding protein. The HSV-1 alpha gene product ICP4 was necessary for this induction, and it was found to be most efficient at a low multiplicity of infection. Functional expression of four genes was demonstrated in that the cell lines complemented infecting HSV-1 temperature-sensitive mutants. The same genes were not available for homologous recombination with infecting virus, however, since no recombinant wild-type virus could be detected. These data demonstrate that HSV-1 beta and gamma genes can be transcribed in the absence of alpha functions in mammalian cells, but that they still respond to HSV-1 regulatory signals such as the alpha gene product ICP4.

Fine structure physical map locations of alterations that affect cell fusion in herpes simplex virus type 1

Fine structure physical map locations were determined for syncytial mutants (MP, syn-20, syn-102, syn-103, and syn-105) of Herpes Simplex Virus type 1 (HSV-1). All except MP were derived from the KOS strain. MP contains multiple mutations, including one that leads to the loss of accumulation of glycoprotein gC (Ruyechan et al., J. Virol. 29, 677-697, 1979). Overlapping DNA subclones within the prototypic map coordinates 0.707 to 0.810 were constructed from a library of KOS fragments. These were used along with intact mutant DNA to rescue the syn marker. Mutations in all of the mutants were rescued by KOS DNA sequences between 0.732 and 0.745. This cell-dependent syn mutation is the only lesion in the KOS-derived mutants. A second syn mutation in MP was mapped at coordinates 0.745 to 0.753. This lesion produces less fusion and is also cell-type dependent for the fusion phenotype. Cell-type independent fusion requires the presence of both mutations. The locus determining glycoprotein C (gC) production in strain MP was also mapped, using indirect immunofluorescence, to coordinates 0.745 to 0.753. Nucleotide sequences for ICP-27, an immediate early or alpha protein of unknown function, are within these coordinates. Since gC production and the syn phenotype are separable by recombination, they must be caused by independent mutations.

The use of monoclonal antibodies to differentiate isolates of herpes simplex types 1 and 2 by neutralisation and reverse passive haemagglutination tests

Monoclonal antibodies specific for herpes simplex type 1 or type 2 were used in reverse passive haemagglutination tests or infectivity neutralisation tests to serotype 100 isolates of herpes simplex virus (HSV). All isolates were independently serotyped by measuring their sensitivity to bromovinyl deoxyuridine. Reverse passive haemagglutination tests with type-specific antibodies directed against the HSV glycoprotein D and major DNA binding protein gave results in perfect agreement with the results of drug-sensitivity measurement. A single isolate behaved anomalously in the neutralisation test with a type 1-specific antibody directed against glycoprotein A/B. Restriction-enzyme analysis of virus DNA suggests that this isolate contains a variant glycoprotein A/B. The two methods used for serotyping proved very sensitive, giving adequate results with samples containing as little as 100 plaque forming units (pfu) of HSV. The reverse passive haemagglutination test has the additional advantages of speed and simplicity.

Insertion mutants of herpes simplex virus have a duplication of the glycoprotein D gene and express two different forms of glycoprotein D

We produced insertion mutants of herpes simplex virus (HSV) that contain two functional copies of genes encoding different forms of glycoprotein D (gD). These viruses have the gene for HSV type 2 (HSV-2) gD at the normal locus and the gene for HSV-1 gD inserted into the thymidine kinase locus. Results of immunoprecipitation experiments done with monoclonal antibodies revealed that both gD genes were expressed by these viruses, regardless of orientation of the inserted HSV-1 gD gene, and that maximal synthesis of both glycoproteins depended on viral DNA replication. This apparently normal expression of the inserted HSV-1 gD gene was from a DNA fragment (SacI fragment, 0.906 to 0.924 map units) containing nucleotide sequences extending from approximately 400 base pairs upstream of the 5' end of the gD mRNA to about 200 base pairs upstream of the 3' end. The glycoproteins expressed from both genes were incorporated into the surfaces of infected cells. Electrophoretic analyses of purified virions and neutralization studies suggest that both glycoproteins were also incorporated into virions. This nonpreferential utilization of both gene products makes these viruses ideal strains for the generation and characterization of a variety of mutations.

Expression of herpes simplex virus beta and gamma genes integrated in mammalian cells and their induction by an alpha gene product

The proteins of herpes simplex virus type 1 (HSV-1) form three kinetic groups termed alpha, beta, and gamma, whose synthesis is regulated in a cascade fashion. alpha products are synthesized first during infection, and they are required for synthesis of beta and gamma proteins. To examine the expression of several HSV-1 beta and gamma genes in the absence of alpha functions, we transferred into mammalian cells a plasmid containing a region of the HSV-1 genome that codes for only beta and gamma genes (0.315 to 0.421 map units). We found stable integration of at least one copy of the intact plasmid in each cell line. Four HSV-1 transcripts of the beta and gamma classes were transcribed constitutively in the cells, including the genes for glycoprotein B and DNA-binding protein. No constitutive synthesis of these two proteins could be demonstrated, however. The integrated HSV-1 genes responded to viral regulatory signals in that they could be induced by infection with HSV-1 mutants resulting in a high level of synthesis of both glycoprotein B and DNA-binding protein. The HSV-1 alpha gene product ICP4 was necessary for this induction, and it was found to be most efficient at a low multiplicity of infection. Functional expression of four genes was demonstrated in that the cell lines complemented infecting HSV-1 temperature-sensitive mutants. The same genes were not available for homologous recombination with infecting virus, however, since no recombinant wild-type virus could be detected. These data demonstrate that HSV-1 beta and gamma genes can be transcribed in the absence of alpha functions in mammalian cells, but that they still respond to HSV-1 regulatory signals such as the alpha gene product ICP4.

Genetic and phenotypic analysis of herpes simplex virus type 1 mutants conditionally resistant to immune cytolysis

Nine temperature-sensitive (ts) mutants of herpes simplex virus type 1 selected for their inability to render cells susceptible to immune cytolysis after infection at the nonpermissive temperature have been characterized genetically and phenotypically. The mutations in four mutants were mapped physically by marker rescue and assigned to functional groups by complementation analysis. In an effort to determine the molecular basis for cytolysis resistance, cells infected with each of the nine mutants were monitored for the synthesis of viral glycoprotein in total cell extracts and for the presence of these glycoproteins in plasma membranes. The four mutants whose ts mutations were mapped were selected with polypeptide-specific antiserum to glycoproteins gA and gB; however, three of the four mutations mapped to DNA sequences outside the limits of the structural gene specifying these glycoproteins. Combined complementation and phenotypic analysis indicates that the fourth mutation also lies elsewhere. The ts mutations in five additional cytolysis-resistant mutants could not be rescued with single cloned DNA fragments representing the entire herpes simplex virus type 1 genome, suggesting that these mutants may possess multiple mutations. Complementation tests with the four mutants whose ts lesions had been mapped physically demonstrated that each represents a new viral gene. Examination of mutant-infected cells at the nonpermissive temperature for the presence of viral glycoproteins in total cell extracts and in membranes at the cell surface demonstrated that (i) none of the five major viral glycoproteins was detected in extracts of cells infected with one mutant, suggesting that this mutant is defective in a very early function; (ii) cells infected with six of the nine mutants exhibited greatly reduced levels of all the major viral glycoproteins at the infected cell surface, indicating that these mutants possess defects in the synthesis or processing of viral glycoproteins; and (iii) in cells infected with one mutant, all viral glycoproteins were precipitable at the surface of the infected cell, despite the resistance of these cells to cytolysis. This mutant is most likely mutated in a gene affecting a late stage in glycoprotein processing, leading to altered presentation of glycoproteins at the plasma membrane. The finding that the synthesis of both gB and gC was affected coordinately in cells infected with six of the nine mutants suggests that synthesis of these two glycoproteins, their transport to the cell surface, or their insertion into plasma membranes is coordinately regulated.