Regulation of herpesvirus macromolecular synthesis. I. Cascade regulation of the synthesis of three groups of viral proteins

Herpes simplex virus infections

Infections with herpes simplex virus (HSV) are extremely common. HSV infection may be asymptomatic or may cause any one of a wide variety of disease syndromes. In this review, the physical properties and mode of replication of HSV are briefly described, and an outline of the different clinical manifestations associated with HSV infection is presented. Principles of diagnosis, treatment, and prevention of these infections are also discussed.

Expression of hepatitis B virus S gene by herpes simplex virus type 1 vectors carrying alpha- and beta-regulated gene chimeras

The domain of the hepatitis B virus (HBV) S gene specifying the HBV surface antigen (HBsAg) and comprising 25 base pairs of the 5'-transcribed noncoding region, the structural gene sequences, and the 3'-noncoding gene sequences including the polyadenylylation site was fused to the promoter-regulatory regions of the beta-thymidine kinase and of the alpha 4 gene of herpes simplex virus type 1 (HSV-1). The chimeric constructs were then inserted into the HSV-1 genome and specifically into the thymidine kinase gene by homologous recombination through flanking sequences. Cells infected with recombinants carrying the chimeric genes produced and excreted the HBsAg into the extracellular medium for at least 12 hr concurrently with the multiplication of the HSV-1 vector. The temporal patterns of expression and the observation that HBV S gene linked to the HSV-1 alpha promoter-regulatory region was regulated as an HSV-1 alpha gene indicate that the HBsAg gene chimeras inserted into the virus were regulated as viral genes. The HBsAg banded in isopycnic CsCl density gradients at a density of 1.17 g/cm3. Electron microscopic studies revealed that HBsAg harvested from the extracellular medium and banded in CsCl density gradients contained spherical particles 15-22 nm in diameter, characteristic of empty HBV envelopes. The results indicate that HSV-1 is a suitable vector for the expression of foreign genes placed under the control of HSV promoter-regulatory regions.

Evidence for translational regulation of herpes simplex virus type 1 gD expression

We compared the rates of synthesis of herpes simplex virus type 1 glycoproteins C and D and quantitated the accumulation of translatable mRNA for each glycoprotein at various times after infection. The rate of synthesis of gD increased sharply early in the infection, peaked by 4 to 6 h after infection, and declined late in the infection. In contrast, the rate of synthesis of gC increased steadily until at least 15 h after infection. The levels of mRNA for both of these glycoproteins, as detected by hybridization and by translation in vitro, continued to increase until at least 15 or 16 h after infection. Synthesis of both gC and gD and their respective mRNAs was found to be sensitive to inhibition of viral DNA replication with phosphonoacetic acid. The finding that reduced amounts of gD were synthesized late in the replicative cycle, whereas gD mRNA continued to accumulate in the cytoplasm, argues that the synthesis of gD is regulated, in part, at the level of translation.

Antibody to early and late antigens of herpes simplex virus type 1 in patients with oral cancer

HEp-2 cells were infected with herpes simplex virus type 1 (HSV-1) and harvested at selected times thereafter. IgG, IgA, and IgM antibody to virus antigens present in these cells at each time was measured in sera from oral cancer patients, and in matched controls. The IgA response of oral cancer patients was significantly greater than that of controls both at 8 and at 48 hours after infection, but showed no difference in response to HSV-1 virus particles. IgM antibody detected two peaks of antigen synthesis, at 4 and 48 hours after infection. Oral cancer patients had a stronger IgM response than did controls to both early and late peaks; the latter was significant at the 5% level. Oral cancer patients also had a significantly higher IgM response to the virus particle. These results imply the existence of at least two different HSV-1 antigens associated with oral cancer. Both are late antigens; one is recognized by IgA, and the other is recognized by IgM antibody.

Separation of sequences defining basal expression from those conferring alpha gene recognition within the regulatory domains of herpes simplex virus 1 alpha genes

The genes of herpes simplex virus 1 form three major groups--alpha, beta, and gamma--whose expression is coordinately regulated and sequentially ordered in a cascade fashion. To determine how the infected cell differentiates between these gene groups, alpha-regulated chimeric genes were constructed in earlier studies by fusing the structural sequences of the thymidine kinase (TK) gene, a beta gene, to the 5' noncoding sequences of alpha genes. These studies showed that (i) one or more structural components of the virion act in trans to increase alpha gene expression and (ii) the 5' noncoding sequences of alpha genes contain cis-acting domains that promote gene expression and confer alpha-gene regulation. These two domains could be moved independently, but the regulatory domain required a promoter for its function. We report here the properties of three sequences containing features common to the regulatory regions of all alpha genes. Sequence 1, containing (G + C)-rich inverted repeats, increased the basal level of TK expression when fused 5' to either the alpha gene 4 promoter or the truncated beta TK promoter. The effect was to some extent orientation dependent. Moreover, sequence 1 restored beta regulation to the truncated beta TK promoter but did not confer alpha-specific regulation on any of the chimeric genes tested. Sequences 2 (49 base pairs) and 3 (29 base pairs), containing an (A + T)-rich homolog from alpha gene 27 and alpha gene 0, respectively, restored alpha-specific regulation to the alpha promoter gene but only sequence 2 conferred alpha regulation on the truncated beta promoter gene. Our results indicate that (i) in natural beta TK the promoter and regulatory domains overlap, (ii) sequence 1 determines basal level of expression and substitutes for a promoter component that is essential for beta but not alpha regulation, and (iii) conversion of a gene with a promoter into an alpha gene requires two elements. Sequence 2 may contain both whereas sequence 3 contains only one.

Transactivation of a late herpes simplex virus promoter

We have asked whether the promoter for the gene encoding the major capsid protein (VP5) of herpes simplex virus functions in uninfected mouse cells. Our experimental strategy was to first fuse the VP5 promoter to the herpes simplex virus thymidine kinase (TK) structural sequence and then to use the resulting hybrid gene to transform TK- cells to TK+. The recombinant gene transferred TK at an extremely low frequency by comparison with the wild-type TK gene, and the TK transcripts present within the resulting rare transformants initiated within the TK structural gene, rather than in the vicinity of the VP5 promoter. However, after infection with herpes simplex virus, large amounts of RNA driven from the VP5 promoter accumulated. We conclude that the VP5 promoter does not function in uninfected cells but is efficiently activated by virally coded factors, most likely one or more immediate-early proteins.

Effects of deletions on expression of the herpes simplex virus thymidine kinase gene from the intact viral genome: the amino terminus of the enzyme is dispensable for catalytic activity

We have transferred two deletions affecting the 5' end of the herpes simplex virus thymidine kinase (TK) gene into the intact viral genome. One, extending from -12 to +189, had no effect on TK mRNA synthesis and only a small effect on TK activity, although the first 27 codons of the TK polypeptide were deleted. The other, extending from -85 to +85, severely impaired TK mRNA synthesis. We conclude that the amino terminus of the TK polypeptide is dispensable for catalytic activity, and that expression of TK in viral infections requires some of the same promoter elements used in uninfected cells.

Temporal regulation of murine cytomegalovirus transcription and mapping of viral RNA synthesized at immediate early times after infection

The replication of murine cytomegalovirus strain Smith in murine embryonic fibroblasts was investigated at immediate early, early, and late times after infection. Cloned subgenomic HindIII fragments of murine cytomegalovirus DNA served to define the regions of transcription. At immediate early times viral RNA classes ranging in size from 5.1 to 1.05 kilobases (kb) were transcribed mainly from the fragments HindIII-K and -L, whereas low levels of transcription were detected from the two termini HindIII-E and HindIII-N. A characteristic pattern of proteins could be translated from immediate early RNA in vitro. At early and late times after infection transcription from all HindIII fragments occurred, but different patterns of transcripts and proteins could be identified. Inhibitors of DNA synthesis induced differences in the late transcription pattern, located in the HindIII-F fragment. The coding region for abundant immediate early transcription could be located at between 0.769 and 0.817 map units. A plasmic clone containing the main part (0.769 to 0.815 map units) of this region was constructed. This region coded for six polyadenylated immediate early RNA species of 5.1, 2.75, 2.0, 1.75, 1.65, and 1.05 kb in size. Only the 1.75-kb RNA originated entirely from the HindIII-L fragment. The 5.1- and 2.75-kb RNA species were encoded by both the HindIII-L and HindIII-K fragments, and the 2.0-, 1.65-, and 1.05-kb RNA species were entirely transcribed within HindIII-K.

Transactivation of a late herpes simplex virus promoter

We have asked whether the promoter for the gene encoding the major capsid protein (VP5) of herpes simplex virus functions in uninfected mouse cells. Our experimental strategy was to first fuse the VP5 promoter to the herpes simplex virus thymidine kinase (TK) structural sequence and then to use the resulting hybrid gene to transform TK- cells to TK+. The recombinant gene transferred TK at an extremely low frequency by comparison with the wild-type TK gene, and the TK transcripts present within the resulting rare transformants initiated within the TK structural gene, rather than in the vicinity of the VP5 promoter. However, after infection with herpes simplex virus, large amounts of RNA driven from the VP5 promoter accumulated. We conclude that the VP5 promoter does not function in uninfected cells but is efficiently activated by virally coded factors, most likely one or more immediate-early proteins.

Early interactions between human cytomegalovirus and cells

Adsorption of cytomegalovirus (CMV) to human fibroblasts was not inhibited by preincubation with other herpes viruses (HSV-1, HSV-2, VZV). Transport of virus to the nucleus was studied using virus labelled with 3H-thymidine. Radioactivity was found in the nucleus 20 minutes after virus had been added to the cells. In order to assess the expression of the virus genome, synthesis of early (EA) and late (LA) antigens was studied. Assayed on permissive human lung fibroblasts, a plaque purified virus contained more EA inducing than both EA and LA inducing viral units. Since this was a consistent finding with virions of all densities, it seems to be an effect of viral dose rather than of virion density. Alternatively, LA-defectiveness is a virion property which does not vary with virion density.

A post-alpha gene function turns off the capacity of a host protein to bind DNA in cells infected with herpes simplex virus 1

HEp-2 cell proteins electrophoretically separated in denaturing polyacrylamide gels and electrically transferred to nitrocellulose sheets contain a polypeptide which efficiently binds linear native DNA end labeled with 32P but not denatured DNA. The polypeptide has an apparent molecular weight of ca. 130,000. The activity of the protein was stable, and no appreciable turnover was observed after exposure of uninfected cells to inhibitory concentrations of cycloheximide for intervals of up to 24 h. However, the activity was absent from lysates of cells harvested 6 h or later postinfection with wild-type viruses. To identify the viral function involved in the loss of DNA-binding activity, we tested the lysates of cells infected with several mutants. Thus, the DNA-binding activity was unaffected in cells infected with a temperature-sensitive mutant (herpes simplex virus 1 tsLB2) in the alpha 4 gene and was maintained at a nonpermissive temperature (39 degrees C). Experiments involving (i) temperature shift-down of cells infected with tsLB2 in the presence of cycloheximide, (ii) withdrawal of cycloheximide in the presence and absence of actinomycin D from cells infected with wild-type virus, (iii) infection of cells at 33 and 39 degrees C with herpes simplex virus 1 tsHA1 carrying a temperature-sensitive lesion in the beta 8 gene, and (iv) infection of cells in the presence of inhibitory concentrations of phosphonoacetate led to the conclusion that the viral functions responsible for the loss of DNA-binding capacity were specified by either beta or gamma genes not dependent on viral DNA synthesis for their expression.

The characterization and purification of DNA binding proteins present within herpes simplex virus infected cells using monoclonal antibodies

Hybridomas secreting monoclonal antibodies against herpes simplex virus (HSV) DNA binding proteins (DBP) have been produced. Five HSV DBP have been characterized according to molecular weight, affinity for DNA, kinetic class and localization within the infected cell. By preparing an immunoadsorbent column from antibody TI8, its specific DBP was purified to apparent homogeneity. The purified DBP retained the ability to bind to DNA.

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.

Antiviral activity of SK&F 21681 against herpes simplex virus

SK&F 21681 (3,10-dimethyl-10-H-s-triazolo[4',3':2,3]-as-triazino-[ 5,6-b]indole) is an inhibitor of the growth of herpes simplex viruses types 1 and 2 at a concentration of 60 micrograms/ml. It inhibits the synthesis of the viral DNA and the formation of virus particles, although the viral polypeptide synthesis is not significantly affected by this compound. Mutants of herpes simplex viruses types 1 and 2 which are able to grow in the presence of SK&F 21681 were isolated. They induced normal levels of thymidine kinase and DNA polymerase activities in the infected cells and did not show resistance to either 9-[2-hydroxyethoxymethyl] guanine or phosphonoacetic acid.

Predominant immediate-early transcripts of human cytomegalovirus AD 169

Transcription of the human cytomegalovirus genome (strain AD 169) was investigated at the immediate-early (IE) time after infection, by using cycloheximide to suppress virus-specific protein synthesis. In total cell RNA, four predominant IE transcripts were found which were encoded by one contiguous region of the long unique segment between map units 0.06 and 0.16 in prototype arrangement of human cytomegalovirus AD 169 DNA. Analysis by Northern blot hybridizations demonstrated that the transcripts possessed a size of 1.9, 2.2, 2.3, and 5.0 kilobases, respectively. Coding sequences and directions of transcriptions were mapped by Northern blots and hybridizations with oligodeoxythymidylic acid-primed and randomly primed cDNA. The 1.9-, 2.2-, and 2.3-kilobase RNAs were found in the polyadenylated fraction of IE RNA exclusively; in contrast, a part of the 5.0-kilobase RNA appeared polyadenylated, although the majority of the same transcript was found in the nonpolyadenylated pool. Also, different from the other IE genes, the DNA coding for the 5.0-kilobase IE RNA was transcribed in high quantities during the late phase of virus replication, suggesting an exemption from the temporal regulation of herpesvirus transcription.

Class-specific antibody responses to early and late antigens of varicella and herpes simplex viruses

Antibody responses to early antigens of varicella-zoster virus (VZV), simian varicella virus, and herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) were studied in primary, secondary, and latent infections. IgG antibody responses to the early antigens occurred in primary and secondary VZV and HSV infections, and antibodies to early antigens were also demonstrable in healthy individuals with latent VZV and HSV infections, indicating that the presence of antibodies to early antigens cannot be taken as evidence of active infection with the viruses. Patients with current VZV or HSV infections showed heterotypic IgG antibody responses to early antigens of VZV and HSV to the same extent as to late antigens. In all groups of patients, IgG antibody titers to early antigens were similar to those against the corresponding late antigens, and no difference was seen in the reactivity of early antigens produced with four different blocking agents (cytosine arabinoside, bromodeoxyuridine, trisodium phosphonoformate, and cycloheximide). Antibodies of the IgM and IgA classes reacted with both early and late antigens of HSV, but only with late antigens of VZV and simian varicella virus, suggesting that these antibodies may be directed against late proteins that are expressed to a greater extent in HSV-infected cells treated with blocking agents than they are expressed in treated VZV-infected cells. Homologous IgM antibody responses occurred in both primary and secondary VZV infections, but only in primary HSV infections. Heterotypic IgM responses to HSV-2 antigen were noted in a few VZV patients who did not have demonstrable IgG antibody to HSV, suggesting that even in patients without prior experience with HSV, a VZV infection may stimulate the production of IgM antibodies that react with antigens that are shared by VZV and HSV-2. IgA antibodies to late antigens of VZV and HSV were demonstrable in latent, as well as active, infections with these viruses.

Analysis of the herpes simplex virus genome during in vitro latency in human diploid fibroblasts and rat sensory neurons

We have previously designed in vitro model systems to characterize the herpes simplex virus type 1 (HSV-1) genome during in vitro virus latency. Latency was established by treatment of infected human embryo lung fibroblast (HEL-F) cells or rat fetal neurons with (E)-5-(2-bromovinyl)-2'-deoxyuridine and human leukocyte interferon and was maintained by increasing the incubation temperature after inhibitor removal. Virus was reactivated by reducing the incubation temperature. We have now examined the HSV-1-specific DNA content of latently infected HEL-F cells and rat fetal neurons treated with (E)-5-(2-bromovinyl)-2'-deoxyuridine and human leukocyte interferon and increased temperature. The HEL-F cell population contained, on an average, between 0.25 and 0.5 copies of most, if not all, HSV-1 HindIII and XbaI DNA fragments per haploid cell genome equivalent. In contrast, the latently infected neurons contained, on an average, 8 to 10 copies per haploid cell genome equivalent of most HSV-1 BamHI DNA fragments. There was no detectable alteration in size or molarity of the HSV-1 terminal or junction DNA fragments obtained by HindIII, XbaI, or BamHI digestion of the latently infected neuron or HEL-F cell DNA, as compared with digestion of a reconstruction mixture of purified HSV-1 virion and HEL-F cell DNAs. These data suggest that the predominant form of the HSV-1 genome in either latently infected cell population is nonintegrated, linear, and nonconcatameric.

Early inhibition of acetylcholinesterase and choline acetyltransferase activity in herpes simplex virus type 1 infection of PC12 cells

Early in the course of productive Herpes simplex virus type 1 (HSV-1) infection of PC12 cells, activities of both acetylcholinesterase (AChE) and choline acetyltransferase (CAT) fell. Studies using metabolic inhibitors and a temperature-sensitive mutant of the virus suggested that the decline in activities of both enzymes was associated with events occurring early in the replicative cycle related to expression of the immediate-early (alpha) group of viral polypeptides. HSV-1 gene products thus may alter specialized cell functions well before the production of viral progeny and initiation of cell lysis. The early clinical manifestations of nervous system viral infection may reflect focal metabolic disturbance rather than, or in addition to, simple cell death.

The cytolytic T lymphocyte response to the murine cytomegalovirus. II. Detection of virus replication stage-specific antigens by separate populations of in vivo active cytolytic T lymphocyte precursors

During the acute cytolytic T lymphocyte (CTL) response of mice to infection with the murine cytomegalovirus two independent populations of activated interleukin-receptive CTL precursors can be demonstrated. One population is specific for cell membrane-incorporated viral structural antigens, whereas the second population detects an antigen, whose appearance is correlated with the synthesis of viral immediate early proteins. Since this new type of antigen is only defined by lymphocyte recognition, it is referred to as the lymphocyte-detected immediate early antigen (LYDIEA). Expression of immediate early antigen precedes the production of viral progeny and, therefore, it is possible that LYDIEA-specific CTL could serve as indicator cells for the very first activities of the viral genome, even during nonproductive infection.

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.

Mutations in the major DNA-binding protein gene of herpes simplex virus type 1 result in increased levels of viral gene expression

We have examined the effect of temperature-sensitive mutations in the herpes simplex virus 1 DNA-binding protein gene on viral gene expression. We have found that at the nonpermissive temperature, the synthesis of certain immediate early, early, and late viral polypeptides was greater in cells infected with the temperature-sensitive mutants than in cells infected with the wild-type virus. This effect was independent of the requirement for this viral protein for viral DNA replication. The altered rate of synthesis of viral proteins was due to a thermolabile gene product. Cells infected with these mutants at the permissive temperature and then shifted to the nonpermissive temperature exhibited enhanced levels of viral gene expression. The addition of actinomycin D at the time of the temperature shift prevented the alteration in viral protein synthesis. Therefore, continuing transcription is required for this change in gene expression. Northern blot analysis of cytoplasmic RNA showed that the steady-state level of specific viral transcripts expressed from parental virus genomes was greater in cells infected by these mutants at the nonpermissive temperature. These results indicate that the major DNA-binding protein of herpes simplex virus type 1 acts as a negative regulator of viral gene expression by affecting the abundance of cytoplasmic viral mRNAs.

Presence of antibodies against herpes simplex virus-specific antigens in human serum

Sera from 110 healthy pregnant women in the third trimester and from 47 controls matched for age, sex and socio-economic status were tested for the presence of antibodies to three antigenic preparations believed to contain mainly alpha, beta, and gamma polypeptides of herpes simplex virus (HSV) type I. Sixty-five of the 110 pregnant women and 22 of the 47 controls possessed antibodies against HSV immediate early antigen, or alpha polypeptides. Among them, three women possessed antibodies against immediate early antigen only. The pregnant group had significantly more women with antibody against all of the three antigenic preparations (60/110) than did the control group (18/47). We conclude that in some women only early genetically determined viral products were produced and that the pregnant state affected the genetic expression of latently infecting HSV.

Blocked herpes simplex virus type 2-specific DNA synthesis in simian virus 40-transformed hamster cells permissive for herpes simplex virus type 1

Simian virus 40-transformed hamster cells (LL-1) permissive to herpes simplex virus type 1 (HSV-1) were shown to be relatively nonpermissive to HSV-2. When LL-1 cells were infected with HSV-2, there was a 3- to 4-log reduction in infectious viral progeny at 24 h postinfection as compared with HSV-1 under identical cultured conditions. HSV-2 could be carried in the LL-1 cell line for up to 12 passages without any appreciable cytopathology. Various early functions of the replicative cycle of HSV-2 appeared to be normal. Experiments demonstrated that early enzyme activity, HSV-2 thymidine kinase, and DNA polymerase appeared at permissive levels in extracts of HSV-2-infected LL-1 cells. However, DNA analysis of HSV-2 infected LL-1 cells demonstrated a block in HSV-2-specific DNA synthesis, although HSV-2 was capable of inhibiting DNA synthesis in LL-1 cells. Furthermore, indirect immunofluorescence studies indicate that late HSV-2 structural protein synthesis was inhibited in infected LL-1 cells. Thus, the inability of HSV-2 to replicate in LL-1 cells is due to a block at or before HSV-specific DNA synthesis, resulting in a reduction of the structural protein synthesis required for viral maturation.

Positive control of the herpes simplex virus thymidine kinase gene requires upstream DNA sequences

We examined the ability of deleted versions of the herpes simplex virus type 1 thymidine kinase gene, present in biochemically transformed mouse cells, to be induced in trans to a higher level of expression by superinfecting herpes simplex virus immediate early gene products. The results demonstrate that sequences mapping between -200 and -80 and between -70 and -12 are required for induction. As these regions are largely coincident with the previously identified thymidine kinase gene promoter, the results suggest that herpes simplex virus immediate early gene products or their metabolic product activate thymidine kinase expression by acting at the promoter region to increase the rate of transcription.

Thermolabile in vivo DNA-binding activity associated with a protein encoded by mutants of herpes simplex virus type 1

The major DNA-binding protein encoded by several temperature-sensitive mutants of herpes simplex virus type 1 was thermolabile for binding to intracellular viral DNA. The ability of DNase I to release this protein from isolated nuclei was used as a measure of the amount of protein bound to viral DNA. This assay was based upon our previous observation that the fraction of herpesviral DNA-binding protein which can be eluted from nuclei with DNase I represents proteins associated with progeny viral DNA (D. M. Knipe and A. E. Spang, J. Virol. 43:314-324, 1982). In this study, we found that several temperature-sensitive mutants encoded proteins which rapidly chased from a DNase I-sensitive to a DNase I-resistant nuclear form upon shift to the nonpermissive temperature. We interpret this change in DNase I sensitivity to represent the denaturation of the DNA-binding site at the nonpermissive temperature and the association with the nuclear framework via a second site on the protein. The DNA-binding activity measured by the DNase I sensitivity assay represents an important function of the protein in viral replication because three of five mutants tested were thermolabile for this activity. A fourth mutant encoded a protein which did not associate with the nucleus at the nonpermissive temperature and therefore would not be available for DNA binding in the nucleus. We also present supportive evidence for the binding of the wild-type protein to intracellular viral DNA by showing that a monoclonal antibody coprecipitated virus-specific DNA sequences with the major DNA-binding protein.

Proteins specified by African Swine Fever virus. IV. Glycoproteins and phosphoproteins

African Swine Fever virus infected MS cells labeled with radioactive 14C-amino acids, 32Pi or [3H]-glucosamine were examined by high resolution sodium dodecylsulfate polyacrylamide gel electrophoresis and showed 43 infected cell polypeptides. Twenty-one of these proteins were present in the nuclear fraction of infected cells. At least 22 of the infected cell polypeptides induced antibodies during natural infections in swine. The pattern of infected cell polypeptides modified by incorporation of showed prosthetic groups that at least 8 polypeptides were phosphorylated and at least three specific viral glycoproteins (A, B and C) were detected by immunoprecipitation. The most highly glycosylated polypeptide corresponds to the structural viral protein VP51.

Characterization of the herpes simplex virion-associated factor responsible for the induction of alpha genes

Herpes simplex virus (HSV) genes form three groups, alpha, beta, and gamma, whose synthesis is coordinately regulated and sequentially ordered in a cascade fashion. Earlier studies by Post et al. (Cell 24:555-565, 1981) have shown that chimeric genes constructed by fusion of 5' noncoding leader and upstream sequences of alpha genes to the 5' noncoding leader and structural sequences of the viral thymidine kinase (TK), a beta gene, are regulated as alpha genes upon recombination into the viral genome. In cells converted from TK- to TK+ phenotype, these chimeric genes are induced by infection with homologous TK- virus. The induction of the resident chimeric gene does not require viral protein synthesis and is independent of the presence of functional alpha gene 4 product required for the expression of beta genes. In this paper, we report on the properties of the alpha-TK gene chimera resident in converted TK+ murine (L316) and human (I316) cells. Our results were as follows. (i) The pattern of induction of L316 cells exposed to 0.1, 1.0, and 10 PFU per cell suggested that exposure to competent virus is required for induction and that in untreated preparations this virus corresponds to infectious virus. (ii) UV light-irradiated virus was just as effective as untreated virus in inducing alpha-TK chimeras. (iii) HSV-1(HFEM)tsB7 induced the alpha-TK gene chimeras at the nonpermissive (39 degrees C) temperature; at 39 degrees C the parental HSV-1(HFEM)tsB7 capsids accumulate at nuclear pores and do not release viral DNA. (iv) The alpha-TK gene chimeras were not induced by infection with spontaneous TK- mutants of pseudorabies virus and bovine mammillitis virus or with human cytomegalovirus or adenovirus type 2 or by exposure to lysates of HSV-1-infected cells from which the virus was removed by centrifugation. These results indicate that the alpha gene inducer is a virion component located outside the capsid and that its function might be to stimulate the transcription of alpha genes by recognizing regulatory sites on viral DNAs or host cell products or both.

The alpha promoter regulator-ovalbumin chimeric gene resident in human cells is regulated like the authentic alpha 4 gene after infection with herpes simplex virus 1 mutants in alpha 4 gene

Human TK- 143 cells were converted to TK+ phenotype with a plasmid containing the native herpes simplex virus 1 (HSV-1), thymidine kinase, a beta gene, and a chimeric ovalbumin gene consisting of the coding sequences of the ovalbumin gene linked to the promoter-regulatory region of the HSV-1 alpha 4 gene. Comparison of the synthesis of ovalbumin and the alpha 4 gene product in the converted cells infected with ts mutants in alpha 4 gene and incubated at the permissive (33 degrees C) and nonpermissive (39 degrees C) temperatures revealed the following. (i) The synthesis of both ovalbumin and alpha 4 gene product was transiently induced at the permissive temperature but continued at elevated levels for many hours at the nonpermissive temperature. (ii) The synthesis of both ovalbumin and alpha 4 gene products resumed when the infected cells were shifted from permissive to nonpermissive temperature after the shut-off of alpha protein synthesis. (iii) Although both the beta-TK and alpha 4-ovalbumin chimeric genes were covalently linked on the same plasmid, each was regulated independently. We conclude that alpha gene regulation is determined solely by (a) the inducer and (b) the induction sequence contained in the promoter-regulatory region and not by the location or the higher order structure of the immediate environment of the gene.

Herpes simplex virus mutants defective in the virion-associated shutoff of host polypeptide synthesis and exhibiting abnormal synthesis of alpha (immediate early) viral polypeptides

Six mutants isolated from herpes simplex virus type 1 were judged to be defective with respect to the virion-associated function acting to rapidly shut off host polypeptide synthesis in herpes simplex virus-infected cells. The mutants were capable of proper entry into the cells, but, unlike the parent wild-type virus, they failed to shut off host polypeptide syntehsis in the presence of actinomycin D. They were consequently designated as virion-associated host shutoff (vhs) mutants. In the presence of actinomycin D, three of the mutants, vhs1, -2, and -3, failed to shut off the host at both 34 and 39 degrees C, whereas vhs4, -5, and -6 exhibited a temperature-dependent vhs phenotype. Since the mutants were capable of growth at 34 degrees C, it appeared that the vhs function was not essential for virus replication in cultured cells. Temperature-shift experiments performed with the vhs4 mutant showed that an active vhs function was required throughout the shutoff process and that, once established, the translational shutoff could not be reversed. In the absence of actinomycin D, the mutants induced a generalized, secondary shutoff of host translation, which required the synthesis of beta (early) or gamma (late) viral polypeptide(s). The vhs mutants appeared to be defective also with respect to post-transcriptional shutoff of alpha (immediate early) viral gene expression, since (i) cells infected with mutant viruses overproduced alpha viral polypeptides, (ii) there was an increased functional stability of alpha mRNA in the vhs1 mutant virus-infected cells, and (iii) superinfection of vhs1-infected cells with wild-type virus, in the presence of actinomycin D, resulted in a more pronounced shutoff of alpha polypeptide synthesis from preformed alpha mRNA than equivalent superinfection with vhs1 virus. The data suggest that the synthesis of alpha polypeptides in wild-type virus infections is subject to a negative post-transcriptional control involving viral gene product(s) present in infected cell lysates constituting virus stocks. The vhs1 mutant and possibly other vhs mutants contain a mutation in the gene encoding this function.

Herpes simplex virus latency and reactivation in isolated rat sensory neurons

An in vitro herpes simplex virus type 1 (HSV-1) latency model has been established using neurons isolated from dissociated rat fetus sensory ganglia as the host cell. Rat fetal neuron cells were pretreated for 24 hr at 37 degrees with (E)-5-(2-bromovinyl)-2'-deoxyuridine and human leukocyte interferon, infected with HSV-1 (approximately 2.5 plaque-forming units/cell), and treated for 7 days with the same inhibitor combination. Infectious HSV-1 became undetectable 3 days postinfection and remained undetectable during the remainder of the inhibitor treatment. After removal of inhibitors on day 7, infectious virus remained undetectable for 2-7 days; subsequently, virus replication ensued and neuronal cells were destroyed. Incubation of inhibitor-treated, infected neuron cells at 40.5 degrees after removal of inhibitors resulted in extension of the latent period to at least 15 days. HSV-1 was reactivated from latently infected neurons by reducing the incubation temperature from 40.5 to 37 degrees and virus-specific cytopathology was observed in neurons within 96 hr after reducing temperature. This in vitro model system will provide the first system to analyze, in a primary cell type of neuronal origin, the state of the HSV genome during establishment and maintenance of the latent state and during virus reactivation.

The major herpes simplex virus DNA-binding protein holds single-stranded DNA in an extended configuration

Properties of the major DNA-binding protein found in herpes simplex virus-infected cells were investigated by using a filter binding assay and electron microscopy. Filter binding indicated that the stoichiometry of binding of the protein with single-stranded DNA is approximately 40 nucleotides per protein molecule at saturation. Strong clustering of the protein in DNA-protein complexes, indicative of cooperative binding, was seen with the electron microscope. Measurements of single-stranded fd DNA molecules saturated with protein and spread for electron microscopy by using both the aqueous and formamide spreading techniques indicated that the DNA is held in an extended configuration with a base spacing of approximately 0.13 nm per base.

Rapid and selective shutoff of plasma protein production in herpes simplex virus type 2-infected hepatoma cells

The effect of herpes simplex virus type 2 (HSV-2) infection of hepatoma McA-RH7777 cells on the production of alpha-fetoprotein (AFP) and several other secreted plasma proteins was examined. Cells infected with HSV-2 were labeled with [35S]methionine for various times postinfection (p.i.). Culture media and intracellular extracts were immunoprecipitated with plasma protein antibodies and examined by polyacrylamide gel electrophoresis. The relative levels of AFP and several other plasma proteins decreased substantially in infected cells compared with mock-treated controls; however, the level of at least one secreted plasma protein was unchanged after infection and the level of another increased after infection. Hybridization analyses with AFP cDNA showed that AFP RNA decreased to 43 and 30% of controls at 3.5 and 6.5 hr p.i., respectively. These observations were supported by the results of cell-free translation of isolated poly(A)-containing RNA. HSV-2 proteins were not detectable at times p.i. when AFP synthesis, secretion, and mRNA levels were significantly diminished. No decrease in AFP levels was observed in cells infected with ultraviolet-irradiated virus. We conclude that HSV-2 infection of McA-RH7777 cells leads to a rapid decrease in synthesis and secretion of specific plasma proteins which is apparent, at least for AFP, at the level of mRNA. This shutoff is not common to all McA-RH7777 cell proteins and, although seen early after infection, most likely requires the expression of a virus gene(s).

Inhibition of glycosylation of herpes simplex virus glycoproteins: identification of antigenic and immunogenic partially glycosylated glycopeptides on the cell surface membrane

The surface membranes of cells infected with herpes simplex virus type 1 (HSV-1), strain KOS, contain three principal glycoproteins, gC (apparent Mr 129k), gB (apparent Mr 120k), and gD (apparent Mr 58k). Infections carried out in the presence of the glycosylation inhibitor 2-deoxy-D-glucose result in the loss of the mature species with the concurrent appearance of lower-molecular-weight polypeptides which are presumably partially glycosylated forms of the fully processed glycoproteins. Specific immunoprecipitation of radiolabeled cytoplasmic extracts of 2-deoxy-D-glucose-inhibited infections identified partially glycosylated proteins designated DG92, DG88, and DG53, which are antigenically related to the corresponding mature forms gB, gC, and gD. Cell surface radioiodination, in combination with specific immunoprecipitation, revealed that DG88 and DG53 were the principal species transported to the cell surface in 2-deoxy-D-glucose-inhibited infections. DG92 was readily detected in the cytoplasm but not on the plasma membrane. Cells infected with the KOS mutant, syn LD70, did not synthesize glycoprotein gC. In glycosylation-inhibited syn LD70 infections, DG88 was not detected in either the cytoplasm or plasma membrane, demonstrating a genetic relationship between DG88 and gC. Polyclonal and monoclonal antibodies directed against the glycoproteins gC, gB, and gD sensitized infected cells to complement-mediated immune cytolysis. Cells infected in the presence of the inhibitor were sensitized to lysis only by antibody specific for gC and gD. The glycosylation-inhibited cells were insensitive to immunolysis by anti-gB monoclonal antibody. These findings confirm that the glycosylation-deficient forms of gC and gD, but not gB reach the cell surface in the presence of inhibitor and that the inhibitor-induced alterations in glycosylation do not cause a complete loss of antigenicity. Inoculation of mice with syngeneic 3T3 cells infected in the presence or absence of inhibitor-induced cytolytic and neutralizing antibody. A major portion of the cytolytic antibody was directed against gC, but anti-gC antibody appeared to play a minor role in virus neutralization. While the serum induced by the control infected cells contained precipitating antibodies for gC, gB, and gD, the serum derived from mice inoculated with inhibitor-treated infected cells had only weak immunoprecipitating activity against gB. Together, these findings have identified partially glycosylated forms of the major HSV glycoproteins and show that complete glycosylation is not required for transport of some of these partially glycosylated polypeptides to the cell surface. Moreover, complete glycosylation of the glycopeptides is not essential for maintenance of antigenicity or immunogenicity, indicating that at least some determinants recognized by antibodies directed against the mature glycoproteins are not affected by 2-deoxy-D-glucose-induced carbohydrate alterations.

Application of denatured, electrophoretically separated, and immobilized lysates of herpes simplex virus-infected cells for detection of monoclonal antibodies and for studies of the properties of viral proteins

We report the use of herpes simplex virus type 1 (HSV-1)- and HSV-2-infected cell polypeptides (ICPs) separated by electrophoresis in polyacrylamide gels and transferred to nitrocellulose to (i) detect monoclonal antibodies to viral polypeptides and to (ii) study the properties of the proteins with the monoclonal antibodies. Our results were as follows. (i) When the antigens were electrophoretically separated in denaturing gels and then immobilized on nitrocellulose strips, we detected a greater diversity of monoclonal antibodies to viral proteins than when we used the technique of immune precipitation of soluble, nondenatured viral antigens. The primary advantage of the technique is in the detection of nonprecipitating antibody and of antibody to poorly soluble antigens not available for reaction in preparations cleared by high-speed centrifugation before immune reaction. (ii) Studies of the viral polypeptides reactive with three monoclonal antibodies indicated that the technique can be used to investigate several properties of the antigens. Specifically, monoclonal antibody to ICP 4 confirmed the accumulation of viral protein in the nucleus and the mapping of the gene in the S component. The results showed, however, that HSV-1 and HSV-2 ICP 4 do have common antigenic determinants. The reaction of a nonprecipitating monoclonal antibody with electrophoretically separated, immobilized polypeptides contained in cytoplasmic and nuclear fractions, those chemically deglycosylated, or those specified by specific HSV-1 x HSV-2 intertypic recombinants identified the antigens reactive with the second monoclonal antibody as various forms of glycoprotein gC. Of particular interest was a set of four antigens, 39,000 to 46,500 in apparent molecular weight, reactive with each of several monoclonal antibodies. These studies showed that two polypeptides partition in the cytoplasm and two in the nucleus and that all comap with the previously mapped ICPs 35 and 37 in the region of the genome defined by the viral thymidine kinase gene on the left and the glycoprotein gA/B gene on the right. Unlike ICP 4 and gC, the four polypeptides are linked by intermolecular bisulfide bonds, inasmuch as the polypeptides were not at the expected locations upon denaturation and electrophoresis in the absence of reducing agents.

Characterization of the herpes simplex virus type 1 glycoprotein D mRNA and expression of this protein in Xenopus oocytes

We have identified and characterized a 3.0 kilobase (kb) mRNA containing coding sequences of the herpes simplex virus type 1 (HSV-1) glycoprotein D (gD) gene. The synthesis of this 3.0 kb mRNA was unaffected by the presence of cytosine arabinoside, but was made in greatly reduced amounts in cells infected with HSV-1 in the presence of cycloheximide: it was, therefore, classified as an early mRNA. By nuclease protection experiments, it was found that the 3.0 kb mRNA is unspliced and, further, that it is 3' co-terminal with a smaller 1.6 kb early mRNA which is transcribed from a DNA sequence 3' to the gD coding sequence. We describe the use of the Xenopus laevis oocyte system to produce HSV-1 gD in vitro. Oocytes injected with mRNA isolated from HSV-1-infected Vero cells synthesized gD, which was identified by immunoprecipitation. Injection of a plasmid clone containing the HSV-1 BamHI J fragment (0.89 to 0.93 map units) into the nuclei of Xenopus oocytes also resulted in synthesis of gD.

Inhibition by vesicular stomatitis virus of herpes simplex virus-directed protein synthesis

Infection of mammalian cells with either herpes simplex virus (HSV) or vesicular stomatitis virus (VSV) results in a marked inhibition of host protein synthesis. These viruses employ different mechanisms to turn off the host. In previous studies we showed that following infection with HSV, cellular mRNA was degraded and host polyribosomes were dissociated (Nishioka and Silverstein, Proc. Nat. Acad. Sci. USA 74, 2370-2374, 1977; Nishioka and Silverstein, J. Virol. 25, 422-426, 1978a). Degradation required synthesis of an HSV-specified polypeptide whereas dissociation appeared to be mediated by a heat-labile virion associated function (Nishioka and Silverstein, J. Virol. 27, 619-627, 1978b). In contrast, when cells are infected with VSV, host mRNAs are not degraded and polyribosome profiles are not drastically altered (Nishioka and Silverstein, 1978a). We have exploited the properties of these two viruses by infecting cells either simultaneously or sequentially in an effort to test our previous hypotheses. Analyses of the distribution of polyribosomes, stability of mRNA, synthesis of mRNA, and patterns of protein synthesis in coinfected cells permit us to conclude that dissociation of polyribosomes in cells infected with HSV results from expression of a virion associated function, degradation of cellular mRNA requires expression of the HSV genome, and VSV is dominant in doubly infected cells because it inhibits de novo transcription of the HSV genome.

Transcription of herpes simplex virus genes in vivo: overlap of a late promoter with the 3' end of the early thymidine kinase gene

We identified in herpes simplex virus type 1-infected cells six cytoplasmic transcripts which were complementary to BamHI restriction endonuclease fragment Q. Two transcripts appeared in major amounts compared with the other four. One major transcript of about 1.4 kilobases was the mRNA for the viral thymidine kinase, was synthesized at intermediate times, and was classified as a beta transcript. The other major transcript was synthesized at late times and was classified as a gamma transcript. This late transcript was about 3 kilonucleotides long and was transcribed in the same direction as the gene for thymidine kinase. The 5' end of this late RNA was located by RNA sequence analysis and was 23 nucleotides downstream from the polyadenylation site for the thymidine kinase mRNA. This finding led to the conclusion that the control region for the 3-kilobase gamma transcript is contained within the 3' untranslated region of the thymidine kinase transcript.

Characterization of herpes simplex virus 2 temperature-sensitive mutants whose lesions map in or near the coding sequences for the major DNA-binding protein

By marker rescue with cloned herpes simplex virus 2 DNA fragments, we have mapped the temperature-sensitive mutations of a series of herpes simplex virus 2 mutants to a region of the herpes simplex virus 2 genome that lies within or near the coding sequences for the major DNA-binding protein, ICP8. In cells infected with certain of these mutants at the nonpermissive temperature, the association of the major DNA-binding protein with the cell nucleus was defective. In these cells, the DNA-binding protein accumulated in the cytoplasmic and the crude nuclear detergent wash fractions. At the permissive temperature, the maturation of the mutant ICP8 was similar to that of the wild-type viral protein. With the remainder of the mutants, the nuclear maturation of ICP8 was similar to that encoded by the wild-type virus at the nonpermissive and permissive temperatures as assayed by cell fractionation.

DNA-binding properties of a herpes simplex virus immediate early protein

The herpes simplex virus alpha, or immediate early, protein ICP4 has been shown to be central to the control of the early stages of virus replication. The detailed mechanism of this control is unknown. In this communication we show that purified ICP4 was unable to bind to DNA even though the protein was capable of such activity in a crude extract. Addition of either infected- or uninfected-cell extracts to the purified protein restored its DNA-binding activity. These results suggest that ICP4 binds to DNA only via a component of uninfected cells.

Detection by RNA blot hybridization of RNA sequences homologous to the BglII-N fragment of herpes simplex virus type 2 DNA

RNA species, extracted at the time of peak synthesis of the alpha, beta, and gamma classes of herpes simplex virus polypeptides from lytically infected Vero cells, were examined for homology to the BglII-N fragment (map units 0.58 to 0.63) of herpes simplex virus type 2 DNA. By using northern blot analysis, two major and several minor polyadenylated RNA species showed homology to the BglII-N fragment at times corresponding to the maximum synthesis of the beta (7 h postinfection) and gamma (12 h postinfection) herpes simplex virus polypeptides. No alpha RNA homologous to the BglII-N fragment was detected.

Structural features of the herpes simplex virus alpha gene 4, 0, and 27 promoter-regulatory sequences which confer alpha regulation on chimeric thymidine kinase genes

Previous studies have shown that herpes simplex virus genes form three groups, alpha, beta, and gamma, whose expression is coordinately regulated and sequentially ordered in a cascade fashion. Chimeric genes constructed by fusion of the coding and 5' nontranslated leader sequences of the thymidine kinase (TK) gene to the sequences upstream from the site of initiation of transcription of alpha genes 4 and 27 are regulated as alpha genes and are induced in cells converted to TK+ phenotype by infection with TK- virus. In alpha gene 4 (S. Mackem and B. Roizman, Proc. Natl. Acad. Sci. U.S.A. 79:4917-4921, 1982), both the promoter and the regulatory region are separable and movable. The promoter permits expression but not induction when fused to TK in the noncoding leader region of the gene. The regulator, when fused to the promoter of an expressible but noninducible portion of the natural beta TK, renders the gene inducible as an alpha gene; it consists of multiple regulatory units acting cumulatively. In this paper, we report on the precise site of initiation of transcription of alpha gene 0 within the inverted b sequences of the L component of viral DNA. We also report the following. (i) The chimeric gene consisting of the coding and 5' nontranslated leader regions of the TK gene fused to portions of the domain of alpha gene 0 extending largely upstream from the site of initiation of transcription of alpha gene 0 was regulated in the same fashion as the alpha 4- and alpha 27-TK chimeras. The regulatory region in the alpha gene 0 is largely upstream from nucleotide - 140. (ii) The promoter-regulatory regions of alpha genes 0, 4, and 27 share TATA sequences, A + T-rich (consensus) sequences occurring in regulating regions of alpha genes 0 and 4 in more than one copy, and multiple G + C-rich inverted repeats. The relation of these sequences to the function of the promoter-regulatory regions of the alpha genes is discussed.

Characterization of two conformational forms of the major DNA-binding protein encoded by herpes simplex virus 1

We have resolved two electrophoretic species of the major DNA-binding protein, infected cell polypeptide 8 (ICP8), encoded by herpes simplex virus 1. In pulse-chase experiments, we observed the conversion of the ICP8a form, the slower migrating species, to the faster migrating form, ICP8b. Thus, the two species appear to be related as precursor-product. The conversion was not due to proteolytic cleavage, because higher concentrations of reducing agents in the sample buffer shifted the faster moving form to the slower moving species. Also, the two forms have identical peptide patterns as analyzed by partial proteolysis in sodium dodecyl sulfate. Thus, the faster moving species appears to be a conformational isomer containing intramolecular disulfide bonds. The functional significance of the two forms of the protein is discussed.

Chicken ovalbumin gene fused to a herpes simplex virus alpha promoter and linked to a thymidine kinase gene is regulated like a viral gene

We are describing a system for the introduction, selection, and expression of eucaryotic genes in higher eucaryotic cells. The carrier consisted of the herpes simplex virus 1 (HSV-1) tk gene covalently linked to an HSV-1 alpha promoter directed away from the tk gene. In this study we fused to the alpha promoter the 5' transcribed noncoding sequences and the coding sequences of the chicken oviduct ovalbumin gene. Cells converted to the TK+ phenotype with this chimeric fragment produced an ovalbumin precursor which was processed and secreted into the extracellular fluid. The ovalbumin gene utilized the HSV-1 alpha promoter and was regulated as a viral gene inasmuch as inversion of the genomic DNA relative to the alpha promoter resulted in no ovalbumin synthesis, and production of ovalbumin was enhanced after superinfection with HSV-1. Synthesis of ovalbumin was not detected when cDNA was linked to the HSV-1 alpha promoter. The carrier system described in this study is suitable for introduction, selection, and expression of eucaryotic genes whose natural promoter is either weak or requires the presence of regulatory elements which may be absent from undifferentiated cells in culture.

Effects of nucleoside analogues on the expression of herpes simplex type 1-induced proteins

Exposure of herpes simplex virus type 1 (HSV-1)-infected Vero cells to the nucleoside analogues 5-iodo-5'-amino-2',5'-dideoxyuridine (AIdUrd), 5-iodo-2'-deoxyuridine (IdUrd) or 5'-amino-2',5'-dideoxythymidine (5'-AdThd) resulted in altered expression of HSV-1-induced proteins. Infected cell proteins (ICPs) synthesized in the presence of the nucleoside analogues were compared by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis to ICPs from non-drug-treated cells and it was found that there was no effect on HSV-1-induced alpha proteins but beta and gamma proteins were reduced as much as 60%. There were three exceptions: ICP 35 (Mr = 46,000) and ICP 39 (Mr = 36,000) were not reduced and ICP 36 (Mr = 42,000) was increased during drug treatment. Progeny virions were isolated from drug-treated infected Vero cells and were compared to progeny isolated from control cells with respect to their polypeptide make-up and for their ability to induce HSV-1 proteins in non-drug-treated Vero cells. The progeny virus from drug-treated cells exhibited altered protein patterns on SDS-polyacrylamide gels with respect to control HSV-1. The progeny virions from AIdUrd- or IdUrd- but not from 5'-AdThd-treated cells were defective in their abilities to induce proteins upon subsequent infection of non-drug-treated Vero cells. Two unusual phosphoproteins were detected; one with an apparent molecular weight of 30,000 was induced by progeny virus from AIdUrd-treated cells and another at approximately 69,000 was induced by progeny virus from 5'-AdThd-treated cells.

Expression of cloned herpesvirus genes. I. Detection of nuclear antigens from herpes simplex virus type 2 inverted repeat regions in transfected mouse cells

Three different recombinant plasmids containing the entire 15-kilobase L and S inverted repeat sequence of herpes simplex virus type 2 DNA have been introduced into cultured Ltk- or BSC cells by both the calcium and DEAE-dextran transfection procedures. In each case, after 24 h approximately 1% of the cells gave strongly positive nuclear staining when assayed by immunofluorescence with hyperimmune antisera made against early and immediate-early infected-cell polypeptides. The nuclear fluorescence pattern and intensity mimicked that observed within 2 to 3 h after infection of Ltk- cells with either herpes simplex virus type 1 or type 2 wild-type virus. Herpes simplex virus type 1 (KOStsB2)-infected Ltk- cells under nonpermissive conditions did not express these antigens in the nucleus. Therefore, we conclude that either one or both of the 185,000- and 110,000-molecular-weight immediate early proteins, or some other as yet unknown gene product encoded entirely within the inverted repeats, can be transiently expressed in large amounts in transfected cells in the absence of other viral genes or accompanying virion components. Permanent mouse cell lines derived from transfection with these plasmids by using the thymidine kinase coselection procedure did not express sufficient nuclear antigen to be detectable by immunofluorescence.