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

Accumulation of viral transcripts and DNA during establishment of latency by herpes simplex virus

Latent infection of mice with wild-type herpes simplex virus is established during an acute phase of ganglionic infection in which there is abundant viral replication and productive-cycle gene expression. Thymidine kinase-negative mutants establish latent infections but are severely impaired for acute ganglionic replication and productive-cycle gene expression. Indeed, by in situ hybridization assays, acute infection by these mutants resembles latency. To assess events during establishment of latency by wild-type and thymidine kinase-negative viruses, we quantified specific viral nucleic acid sequences in mouse trigeminal ganglia during acute ganglionic infection by using sensitive PCR-based assays. Through 32 h postinfection, viral DNA and transcripts representative of the three kinetic classes of productive-cycle genes accumulated to comparable levels in wild-type- and mutant-infected ganglia. At 48 and 72 h, although latency-associated transcripts accumulated to comparable levels in ganglia infected with wild-type or mutant virus, levels of DNA accumulating in wild-type-infected ganglia exceeded those in mutant-infected ganglia by 2 to 3 orders of magnitude. Coincident with this increase in DNA, wild-type-infected ganglia exhibited abundant expression of productive-cycle genes and high titers of infectious progeny. Nevertheless, the levels of productive-cycle RNAs expressed by mutant virus during acute infection greatly exceeded those expressed by wild-type virus during latency. The results thus distinguish acute infection of ganglia by a replication-compromised mutant from latent infection and may have implications for mechanisms of latency.

Transcriptional targeting of herpes simplex virus for cell-specific replication

Tissue- or cell-specific targeting of vectors is critical to the success of gene therapy. We describe a novel approach to virus-mediated gene therapy, where viral replication and associated cytotoxicity are limited to a specific cell type by the regulated expression of an essential immediate-early viral gene product. This is illustrated with a herpes simplex virus type 1 (HSV-1) vector (G92A) whose growth is restricted to albumin-expressing cells. G92A was constructed by inserting an albumin enhancer/promoter-ICP4 transgene into the thymidine kinase gene of mutant HSV-1 d120, deleted for both copies of the ICP4 gene. This vector also contains the Escherichia coli lacZ gene under control of the thymidine kinase promoter, a viral early promoter, to permit easy detection of infected cells containing replicating vector. In the adult, albumin is expressed uniquely in the liver and in hepatocellular carcinoma and is transcriptionally regulated. The plaquing efficiency of G92A is > 10(3) times higher on human hepatoma cells than on non-albumin-expressing human cells. The growth kinetics of G92A in albumin-expressing cells is delayed compared with that of wild-type HSV-1, likely due to aberrant expression of ICP4 protein. Cells undergoing a productive infection expressed detectable levels of ICP4 protein, as well as the reporter gene product beta-galactosidase. Confining a productive, cytotoxic viral infection to a specific cell type should be useful for tumor therapy and the ablation of specific cell types for the generation of animal models of disease.

Induction of transcription by a viral regulatory protein depends on the relative strengths of functional TATA boxes

The mechanisms by which viral regulatory proteins activate the cellular transcription apparatus without binding to specific DNA elements are not fully understood. Several lines of evidence suggest that activation by one such regulatory protein, herpes simplex virus ICP4, could be mediated, at least in part, by TFIID. To test this model, we replaced the TATA box of the ICP4-responsive viral thymidine kinase gene with functional TATA boxes that displayed different apparent affinities for TATA-box-binding protein as measured by DNase I footprinting. We measured the effects of these TATA boxes on ICP4 induction by constructing ICP4-deficient recombinant viruses containing the different TATA alleles and comparing their expression in cells lacking or expressing ICP4. Overall, ICP4 induced weak TATA boxes (those that displayed low apparent affinity for TATA-box-binding protein and low basal expression) the most (18- to 41-fold) and strong TATA boxes the least (7- to 10-fold). Therefore, ICP4 induction correlated inversely with TATA box strength. Using a reconstituted in vitro transcription assay, we determined that the relative levels of induction by ICP4 of the different TATA alleles were similar to those measured in vivo, suggesting that ICP4 was the only viral protein required for induction. These results fit a model in which ICP4 acts in part to enhance binding of TFIID to the TATA box. We compare and contrast these results with those observed with the viral regulatory proteins adenovirus E1a and simian virus 40 large T antigen and the cellular coactivator PC4.

Regulation of herpes simplex virus thymidine kinase in cells treated with a synergistic antiviral combination of alpha interferon and acyclovir

Alpha interferon (IFN-alpha) and acyclovir (ACV) are synergistic in their anti-herpes simplex virus activities. IFN-alpha treatment reduced the herpes simplex virus thymidine kinase (TK) activity present in cells 6 h postinfection, while steady-state levels of TK mRNA remained at or above the amount in infected, untreated cells. The inhibition of TK production by IFN-alpha treatment appeared to be transient and translational, not transcriptional.

Identification and nucleotide sequence of a gene in feline herpesvirus type 1 homologous to the herpes simplex virus gene encoding the glycoprotein H

A gene encoding the glycoprotein H (gH) homologue of feline herpesvirus type 1 was identified and sequenced. It was located immediately downstream of the thymidine kinase gene within an EcoRI 6.6 kbp fragment. In addition, a partial UL21 homologous gene was located downstream of the gH homologous gene. The primary translation product of the gH homologous gene is predicted to consist of 821 amino acids with a molecular weight of 92.5 kDa. It possesses several characteristics typical of transmembrane glycoproteins, including a N-terminal hydrophobic signal sequence, C-terminal transmembrane domain, and putative N-linked glycosylation sites. Analysis of this protein revealed amino acid sequence homologies of 33.1% with equine herpesvirus type 1 (EHV-1) gH, 32.6% with EHV-4 gH, 29.1% with varicella-zoster virus gIII, 28.5% with pseudorabies virus gH, and 25.1% with herpes simplex virus type 1 gH. By Northern blot analysis, one of the transcripts specific for the gH homologous gene might be a mRNA of approximately 3.0 kb.

Sequence and transcript analysis of the bovine herpesvirus 1 thymidine kinase locus

A detailed sequence and transcript analysis of the thymidine kinase (tk) gene of bovine herpesvirus 1 (BHV1, Cooper strain) was carried out. A tk open reading frame (ORF) of 1077 bp was identified and compared with tk ORFs previously published for other strains of BHV1. The Cooper sequence was in good agreement with that of strain Q3932 but differed significantly from strains 6660 and LA. Reanalysis of the LA tk sequence, however, failed to confirm this difference. Except for five single base substitutions, our results indicate that the Cooper, Q3932, and LA strains share the same tk sequence. The size of the tk mRNA was determined by Northern blot analysis. In contrast to the size of other herpesvirus tk mRNAs (approximately 1.5 kb), the BHV1 tk transcript was 4.3 kb. Northern blot analysis indicated that the tk transcript was 3' coterminal with the downstream 3.1-kb transcript which encodes a BHV1 homologue of the HSV1 H glycoprotein (gH). The 5' ends of the tk and gH mRNAs were mapped by S1 analysis to positions 135 and 91 bp upstream of their respective translation start sites. The 5' end of the tk transcript was found to overlap a 5.2-kb transcript with opposite polarity to the tk mRNA.

Construction and properties of a mutant of herpes simplex virus type 1 with glycoprotein H coding sequences deleted

A mutant of herpes simplex virus type 1 (HSV-1) in which glycoprotein H (gH) coding sequences were deleted and replaced by the Escherichia coli lacZ gene under the control of the human cytomegalovirus IE-1 gene promoter was constructed. The mutant was propagated in Vero cells which contained multiple copies of the HSV-1 gH gene under the control of the HSV-1 gD promoter and which therefore provide gH in trans following HSV-1 infection. Phenotypically gH-negative virions were obtained by a single growth cycle in Vero cells. These virions were noninfectious, as judged by plaque assay and by expression of beta-galactosidase following high-multiplicity infection, but partial recovery of infectivity was achieved by using the fusogenic agent polyethylene glycol. Adsorption of gH-negative virions to cells blocked the adsorption of superinfecting wild-type virus, a result in contrast to that obtained with gD-negative virions (D. C. Johnson and M. W. Ligas, J. Virol. 62:4605-4612, 1988). The simplest conclusion is that gH is required for membrane fusion but not for receptor binding, a conclusion consistent with the conservation of gH in all herpesviruses.

Mutational analysis of two herpes simplex virus type 1 late promoters

To investigate the cis-acting sequence elements that are involved in the regulation of herpes simplex virus type 1 late gene expression, linker-scanning mutations were constructed in the promoters of the glycoprotein C and glycoprotein H genes. Each promoter mutation was inserted upstream of the Escherichia coli lacZ gene in a recombinant virus, and the relative activities of beta-galactosidase expressed from individual recombinant viruses were compared. This analysis identified three sequence elements in each promoter: a TATA element, an element that overlapped the start of transcription, and an element downstream from the start of transcription. Primer extension analysis confirmed these results and showed that mutations in either the TATA element or the initiation sequence could eliminate normal transcription initiation. Analysis of expression from hybrid promoters revealed that the TATA and the initiation elements were interchangeable, at least when correctly aligned, and that the initiation element plays a pivotal role in determining the actual site of transcription initiation.

Replacement mutagenesis of the human cytomegalovirus genome: US10 and US11 gene products are nonessential

The US6 gene family, located within the unique short region (US) of the human cytomegalovirus (HCMV) genome, contains six open reading frames (US6 through US11) which may encode glycoproteins, such as gcII (D. Gretch, B. Kari, R. Gehrz, and M. Stinski, J. Virol. 62:1956-1962, 1988). By homologous recombination, several different recombinant HCMV were created which contain a marker gene, beta-glucuronidase, inserted within this gene family. It was demonstrated that beta-glucuronidase has utility as a marker gene for the identification of recombinants in this herpesvirus system, without the occurrence of deletions in other regions of the viral genome. DNA and RNA blot analyses attested to the fidelity of the recombination. Immunoprecipitation experiments using monospecific polyclonal antisera indicated that the US10 and/or US11 gene products were not expressed in the recombinants, as predicted. These results, along with single-cycle growth analyses, indicated that the US10 and US11 gene products are nonessential for virus replication and growth in tissue culture. HCMV recombinants expressing beta-glucuronidase seemed to be genetically stable.

The relative stability of selected herpes simplex virus type 1 mRNAs

The relative stability of herpes simplex virus type 1 mRNAs was investigated by examination of the decay rates of selected viral transcripts. The synthesis of mRNA was inhibited by the addition of dactinomycin to HSV-1 infected cells, and the abundance of individual transcripts was determined at subsequent times by RNA blot hybridization. For two immediate-early mRNAs, those encoding the 110 and 63 kilodalton immediate-early proteins, RNA synthesis was inhibited at 3 h post-infection and mRNA half-lives of 5-7 h were found. Examination at 5 h post-infection of the early mRNA encoding thymidine kinase as well as the late mRNA encoding glycoprotein H revealed half-lives of 8-11 h. In contrast, at 12 h post-infection, the late mRNAs encoding the glycoproteins C, E, as well as H were found to have half-lives of 14-29 h. These findings suggest that the relative stability of viral mRNA increases late in infection and is dependent upon the time after infection rather than being strictly a property of the mRNA itself.

Upstream promoter elements of the herpes simplex virus type 1 glycoprotein H gene

To investigate the cis-acting sequence elements that are involved in the regulation of herpes simplex virus type 1 late-gene expression, recombinant viruses were constructed that express the Escherichia coli lacZ gene from the promoter of the glycoprotein H (gH) gene. Deletion experiments established an upstream boundary for the gH promoter of no more than 83 bp from the start of gH transcription and showed that the promoter sequences did not overlap with coding sequences of the upstream thymidine kinase (tk) gene. Sequences of the tk gene previously shown to be required for efficient processing of the tk transcript were essential for expression form the gH promoter and included a TATA-like element. In addition, the gH TATA element was specifically mutagenized to substitute the TATA elements of immediate-early, early, and other late viral promoters for the gH TATA element. The results indicated that the TATA element was an interchangeable component of herpes simplex virus type 1 promoters and did not regulate temporal expression.

Herpes simplex virus transactivator ICP4 operationally substitutes for the cellular transcription factor Sp1 for efficient expression of the viral thymidine kinase gene

The herpes simplex virus type 1 (HSV-1) ICP4 protein is a transcriptional activator of many eucaryotic RNA polymerase II promoters. The HSV-1 thymidine kinase gene (tk) promoter is induced by ICP4 and contains binding sites for the cellular transcription factors TFIID, Sp1, and CCAAT-binding proteins, each of which affects expression of the tk gene. In this study, the effects of mutations in these sites on the transcription of tk in the presence and absence of ICP4 were determined during viral infection. Only the TATA box was necessary for efficient expression in the presence of ICP4; however, ICP4 apparently can still induce tk transcription even when the TATA box is disrupted. Alteration of the Sp1 sites had a minor effect on ICP4-induced expression in comparison to a large effect in the absence of ICP4, indicating that ICP4 can operationally substitute for the function of the transcription factor Sp1. In addition, tk was still expressed with the kinetics of an early gene in the absence of binding sites for Sp1 and CCAAT-binding proteins.

Cytosine methylation in the EcoRI site of active and inactive herpesvirus thymidine kinase promoters

The herpesvirus thymidine kinase (tk) gene integrated in the human cell line, 2.1-a, can be inactivated by limited de novo methylation. All these TK- clones show partial EcoRI digestion of the recognition site (cGAATTCg) in the tk promoter in contrast to complete digestion of this site in the original cell line. Studies on well-defined substrates prepared in vitro showed that methylation of one cytosine in the EcoRI recognition sequence resulted in partial and methylation of both cytosines in severe inhibition of digestion by EcoRI. This characteristic was used to determine whether no, one or both cytosines in the EcoRI site of the tk promoter were methylated in various TK- clones derived from 2.1-a and in TK+ clones re-expressing the gene after 5-azacytidine treatment. A high correlation was found between inactivity of the tk gene and methylation of only one of the two cytosines in the EcoRI recognition site. The results also show that the tk promoter can be active despite the presence of a methylated cytosine.

Replication of herpes simplex virus type 1 in differentiated human promyelocytic HL-60 cells

The capability of herpes simplex virus type 1 (HSV-1), strain Angelotti (ANG), to replicate in human promyelocytic HL-60 cells treated with 1,2-tetradecanoyl-phorbol-13-acetate (TPA) and dimethyl sulfoxide (DMSO) was examined. Virus titrations and infectious center assays revealed that HSV-1 ANG replicated in nontreated HL-60 cells and in HL-60 cells treated with TPA. An abortive infection was observed in DMSO-stimulated HL-60 cells. Viral DNA synthesis was detected in nontreated and TPA-treated cells, but not in DMSO-treated cells. Analysis of HSV-1 transcripts revealed that albeit the differences in pretreatment, HL-60 cells synthesized viral immediate-early (ICP4) and early (tk and pol) RNAs, whereas a late viral transcript (gC) was almost exclusively detected in nontreated and TPA-treated HL-60 cells. In line with these observations were the results obtained from studies on viral protein synthesis. The immediate-early protein ICP4 was found in all three cell types. Early (pol), delayed-early (gB), as well as late proteins (VP 5, gC) were identified in nontreated and TPA-treated cells, but only in reduced amounts in DMSO-treated cells. These data suggest a translational block of HSV replication in DMSO-treated HL-60 cells at the level of early gene expression.

Control of mRNA stability by the virion host shutoff function of herpes simplex virus

vhs1 is a mutant of herpes simplex virus type 1 that is defective in the virion host shutoff function responsible for the degradation of cellular mRNAs and the concomitant shutoff of host protein synthesis. In this study, the effect of the vhs1 mutation on the metabolism of viral mRNAs was examined by measuring the half-lives and patterns of accumulation of 10 different viral mRNAs representing all kinetic classes. The vhs1 mutation had the effect of dramatically lengthening the cytoplasmic half-lives of all 10 mRNAs. In wild-type virus infections, the 10 mRNAs had similar half-lives, suggesting that little, if any, target mRNA selectivity was exhibited by the vhs function. The vhs1 mutation caused overaccumulation of a number of mRNAs. The effect was most dramatic for the alpha (immediate-early) mRNA for ICP27 and the beta (early) mRNAs encoding thymidine kinase, ICP8, and DNA polymerase. Whereas in wild-type infections these mRNAs increased to peak levels and subsequently declined in abundance, in vhs1 infections they continued to accumulate until late times. A significant but less dramatic overaccumulation was observed for several beta-gamma (delayed-early) and gamma (late) mRNAs. The results suggest that the vhs protein plays an important role in determining the half-lives of viral mRNAs belonging to all kinetic classes and in so doing is important in the normal downregulation at late times of alpha and beta gene expression.

De novo methylation as major event in the inactivation of transfected herpesvirus thymidine kinase genes in human cells

Spontaneous inactivation of integrated thymidine kinase genes was studied in three human cell lines, one with multiple copies and two with a single copy of a transfected shuttle plasmid containing two selectable genes: the HSV tk gene and the Eco gpt gene. Selection for gpt expression prevented the isolation of TK- mutants which are the result of plasmid loss. Under these conditions TK- clones were isolated with a frequency of 5.10(-6) both with the cell line containing 5 or 6 copies of the tk gene and with one of the two cell lines containing one copy of this gene. This inactivity of the tk gene was associated with de novo methylation as the number of HAT-resistant (TK+) clones strongly increased after growth of the TK- derivatives in the presence of the demethylating agent, 5-azacytidine. Digestion with methylation-sensitive restriction enzymes revealed two different patterns of DNA methylation in the genomic DNA of TK- variants. In the TK- derivatives of the cell line containing multiple copies of the tk gene many HpaII restriction sites in the gene copies were insensitive to digestion. These HpaII sites were, however, not methylated in TK- variants of the cell line containing one copy of the plasmid, and methylated CpGs could be detected only with EcoRI which recognizes the cGAATTCg sequence in the tk promoter region. With the other of the two single-copy TK+ cell lines no TK- mutants were obtained, suggesting that the position of a gene in the genome is an important factor in determining the frequency and the extent of de novo methylation. Additionally, we observed that remethylation is an even more efficient process of gene inactivation as TK+ clones reactivated with 5-azacytidine can become TK- again at a 100-fold higher rate than the original TK+ cell line.

Effect of an amber mutation in the herpes simplex virus thymidine kinase gene on polypeptide synthesis and stability

KG111 is a mutant of herpes simplex virus (HSV), strain KOS, that exhibits temperature-dependent drug resistance. For example, it is almost as resistant as a thymidine kinase (tk)-deficient virus at 39 degrees, but is relatively sensitive to acyclovir at 34 degrees, Using marker transfer techniques, we have mapped the mutation conferring temperature-dependent drug resistance in KG111 to the 5' portion of the tk gene. Sequencing of this region revealed an amber mutation at codon 44, which lies between the first and second methionine codons of the tk polypeptide. This mutation is identical to that found in TK4, an HSV mutant derived from Cl 101 (L. Haarr et al., 1985, J. Virol. 56, 512-519). Analyses of immunoprecipitated tk proteins from KG111- and TK4-infected cells showed that KG111 and TK4 do not synthesize full-length tk polypeptides, but instead produce a truncated form of the protein. Small amounts of a similar truncated tk polypeptide are also produced in wild-type-infected cells and are thought to arise from initiation at a downstream AUG. The relative amounts and size of the mutant tk proteins compared with those of the wild-type are consistent with the amber mutation eliminating translation of full-length polypeptide and causing a four- to fivefold increase in the utilization of downstream AUG codons for initiation. The truncated polypeptides specified by KG111 and TK4 are less stable than the full-length polypeptide at 39 degrees, which may contribute to the conditional drug-resistant phenotype. On the other hand, the truncated polypeptides normally expressed by wild-type virus at low levels and the more highly expressed truncated tk polypeptides from a deletion mutant are relatively stable at 39 degrees. These results suggest that stability of the truncated tk polypeptide is influenced by the amount of tk present.

Genetic and phenotypic characterization of mutants in four essential genes that map to the left half of HSV-1 UL DNA

Several HSV-1 proteins including the major capsid protein (VP5), two minor capsid proteins (VP11-12 and VP18.8), the alkaline nuclease and glycoprotein gH have been reported to be encoded by the left-most one-third of HSV-1 UL DNA. In this paper, we present physical mapping data and phenotypic analysis of six ts mutants whose mutations lie within this region and which collectively represent four functional complementation groups (1-6, 1-7, 1-10, and 1-26). In this study, mutants in complementation group 1-10 were found to be defective in the synthesis of viral DNA, late viral polypeptides, and the formation of mature capsid-like structures--properties characteristic of other ts mutants defective in functions required for viral DNA synthesis. Two DNA-positive mutants in complementation group 1-7 fail to induce capsid formation and probably possess mutations in coding sequences for VP5. Mutants in two other complementation groups (1-6 and 1-26) synthesize significant levels of viral DNA, late polypeptides, and capsids. The functions of the gene products represented by these mutants remain to be determined.

Sequences of herpes simplex virus type 1 that inhibit formation of stable TK+ transformants

We have identified two regions of the herpes simplex virus type 1 (HSV-1) genome that inhibit DNA-mediated transformation of thymidine kinase-less L (Ltk-) cells by the cloned HSV-1 tk gene. When plasmids containing the EcoRI fragments EK or JK were mixed at 30 fmol/ml with the tk gene and transfected into Ltk- cells, the frequency of transformation was inhibited 80 to more than 90% relative to the control. Of the remaining 10 EcoRI fragments of the HSV-1 genome, 8 were inactive and 2 were weakly active. A 6.1-kilobase PstI subclone between 0.743 and 0.782 map units was isolated from pEK. This clone, pEK-P3P4, exhibited antitransformation activity toward HSV-1 tk and also the bacterial genes gpt and neo. pEK-P3P4 contains the alpha 27 gene, and restriction endonuclease inactivation and subcloning studies established that alpha 27 alone did not inhibit transformation. However, alpha 27 plus sequences both upstream and downstream of alpha 27 did inhibit transformation. In addition, alpha 0 or alpha 4 could substitute for alpha 27 in effecting antitransformation with these sequences. Therefore, an alpha gene and two additional loci in pEK-P3P4 are required for antitransformation. A second antitransforming locus in the reiterated sequences common to EK and JK and distinct from those in pEK-P3P4 was also identified but not characterized in detail. How antitransformation may be an expression of regulation of viral and host cell gene expression is discussed.

RNA from an immediate early region of the type 1 herpes simplex virus genome is present in the trigeminal ganglia of latently infected mice

Transcription of the type 1 herpes simplex virus (HSV-1) genome in trigeminal ganglia of latently infected mice was studied using in situ hybridization. Probes representative of each temporal gene class were used to determine the regions of the genome that encode the transcripts present in latently infected cells. Probes encoding HSV-1 sequences of the five immediate early genes and representative early (thymidine kinase), early-late (major capsid protein), and late (glycoprotein C) genes were used in these experiments. Of the probes tested, only those encoding the immediate early gene product infected-cell polypeptide (ICP) 0 hybridized to RNA in latently infected tissues. Probes containing the other immediate early genes (ICP4, ICP22, ICP27, and ICP47) and the representative early, early-late, and late genes did not hybridize. Two probes covering approximately equal to 30% of the HSV-1 genome and encoding over 20 early and late transcripts also did not hybridize to RNA in latently infected tissues. These results, with probes spanning greater than 60% of the HSV-1 genome, suggest that transcription of the HSV-1 genome is restricted to one region in latently infected mouse trigeminal ganglia.

Isolation and characterization of PRT1, a gene required for the initiation of protein biosynthesis in Saccharomyces cerevisiae

We isolated a cloned DNA fragment containing PRT1, a gene required for the initiation of protein biosynthesis in Saccharomyces cerevisiae, by complementation of the temperature-sensitive prtl-1 mutation. The entire PRT1 gene is contained within a 3.2-kilobase-pair segment of the cloned DNA in YEp13 H1.2. Southern blot analysis demonstrated that PRT1 is a single copy gene which is transcribed into a 2.3-kilobase RNA. We determined the direction of transcription and mapped the 5' and 3' ends of the gene.

Isolation and characterization of PRT1, a gene required for the initiation of protein biosynthesis in Saccharomyces cerevisiae

We isolated a cloned DNA fragment containing PRT1, a gene required for the initiation of protein biosynthesis in Saccharomyces cerevisiae, by complementation of the temperature-sensitive prtl-1 mutation. The entire PRT1 gene is contained within a 3.2-kilobase-pair segment of the cloned DNA in YEp13 H1.2. Southern blot analysis demonstrated that PRT1 is a single copy gene which is transcribed into a 2.3-kilobase RNA. We determined the direction of transcription and mapped the 5' and 3' ends of the gene.

The promoter for the late gene encoding Vp5 of herpes simplex virus type 1 is recognized by cell extracts derived from uninfected cells

The ability of whole-cell extracts from uninfected HeLa cells to recognize the promoter for the herpes simplex virus type 1 late gene encoding the major capsid protein Vp5 was investigated by using both in vitro transcriptional and S1 nuclease protection analysis. This gene promoter was recognized by the cell extracts and produced abundant amounts of transcript in the absence of any other virus-encoded factors. This transcript was shown to arise, in vitro, from specific initiation at or very near the physiological mRNA start site. Thus, it appears that cell extracts from uninfected HeLa cells can efficiently recognize both early- and late-gene promoters.

A genetic approach to promoter recognition during trans induction of viral gene expression

Viral infection of mammalian cells entails the regulated induction of viral gene expression. The induction of many viral genes, including the herpes simplex virus gene encoding thymidine kinase (tk), depends on viral regulatory proteins that act in trans. Because recognition of the tk promoter by cellular transcription factors is well understood, its trans induction by viral regulatory proteins may serve as a useful model for the regulation of eukaryotic gene expression. A comprehensive set of mutations was therefore introduced into the chromosome of herpes simplex virus at the tk promoter to directly analyze the effects of promoter mutations on tk transcription. The promoter domains required for efficient tk expression under conditions of trans induction corresponded to those important for recognition by cellular transcription factors. Thus, trans induction of tk expression may be catalyzed initially by the interaction of viral regulatory proteins with cellular transcription factors.

The properties and sequence of glycoprotein H of herpes simplex virus type 1

The map position of the coding sequence of glycoprotein H of herpes simplex virus type 1 was determined by marker transfer studies in which DNA fragments cloned from a virus resistant to neutralisation by an anti-gH monoclonal antibody were used to transfer antibody resistance to wild type virus DNA following cotransfection. The gH coding sequence was mapped to the BglII "m" fragment of HSV-1 DNA (map coordinates 0.27-0.312), confirming the map position previously determined by intertypic recombinant analysis (Buckmaster et al., 1984). The complete nucleotide sequence of the BglII "m" fragment revealed two large open reading frames in addition to the thymidine kinase gene. The open reading frame lying immediately 3' of the thymidine kinase gene has a predicted translation product with the features of a large glycoprotein. This open reading frame translates to an amino acid sequence of 90,323 mol wt with a signal peptide, a membrane anchor sequence, a large external domain containing potential N-glycosylation sites, and a charged C- terminal cytoplasmic domain. We suppose that this amino acid sequence corresponds to gH of HSV-1, and A. Davison (personal communication) has noted the existence of homologous glycoproteins predicted from the nucleotide sequences of Varicella-zoster virus and Epstein-Barr virus. The properties of monoclonal antibody LP11, directed against gH show remarkable similarities to the properties for gD antibodies. LP11 efficiently neutralizes virus infectivity, blocks cell fusion by syncytial virus strains, and inhibits the formation of plaques when added to cell monolayers after infection. These similarities in antibody activity imply functional relatedness between gH and gD of herpes simplex virus.

The herpes simplex virus type 2 equivalent of the herpes simplex virus type 1 US7 gene and its flanking sequences

Nucleotide sequencing studies (D. J. McGeoch, A. Dolan, S. Donald, and F. Rixon, 1985, J. Mol. Biol. 181, 1-14) have indicated that herpes simplex virus type 1 (HSV-1) has a coding sequence, referred to as US7, between the genes for the glycoproteins D and E (gD and gE). Northern blot analysis and nucleotide sequencing have been carried out to show that the type 2 virus (HSV-2) has an equivalent to the US7 gene. A comparison with the HSV-1 sequence has revealed some surprising similarities and differences. At the nucleotide level, HSV-2 has inserted a large sequence into the gE promoter, retained a large palindrome present in the coding sequence but not some tandem repeats, and deleted a region beside those repeats. At the amino acid level, the putative transmembrane sequence has been remarkably well conserved, and hydrophobic moment analysis indicates that it could be interacting with polar species within the plane of the membrane. Immediately after the deletion in the HSV-2 sequence, there is an N-glycosylation signal, and HSV-2 has one more such signal than HSV-1. The longest conserved sequence at the nucleotide level codes for a region of polypeptide that is strongly predicted to fold into alpha-helix. Implications of these analyses to the structure and possible function of these molecules are discussed.

Identification by antibody to a synthetic peptide of a protein specified by a diploid gene located in the terminal repeats of the L component of herpes simplex virus genome

In the course of studies on the a sequences located at the termini of and at the junction between the L and S components of herpes simplex virus 1 DNA, J. Chou and B. Roizman (J. Virol. 57:629-637, 1986) noted that the a sequence acted as a gamma 1 promoter when fused to the structural sequence of the thymidine kinase gene, the b inverted repeat sequences located in the L component next to the a sequences contained an open reading frame predicted to encode the protein of 358 amino acids with a molecular weight of 37,054, and the transcription of an RNA homologous to the open reading frame initiated within the a sequence. The nucleotide sequence of the open reading frame predicted the presence of the triplet Ala-Thr-Pro repeated 10 times. To verify the existence of the predicted gene, designated gamma 134.5, a synthetic peptide consisting of the triplet Ala-Thr-Pro repeated 10 times was synthesized and used to raise antibodies in rabbits. The results were as follows. The antiserum to the peptide reacted with a 43,500-apparent-molecular-weight protein present in lysates of cells infected with herpes simplex virus 1 but not present in mock-infected or herpes simplex virus 2-infected cells. We genetically engineered a recombinant virus containing a single copy of a truncated gene. Concordant with predictions, the antibody reacted with a faster-migrating protein in cells infected with this recombinant. The gamma 134.5 gene product was soluble, and it accumulated primarily in the cytoplasm late in infection. The overlap of the domain of the gamma 134.5 gene with the a sequence raises the possibility that it acts in trans on the a sequence and is associated with one of the functions currently ascribed to the a sequences.

DNA sequence of the herpes simplex virus type 1 gene encoding glycoprotein gH, and identification of homologues in the genomes of varicella-zoster virus and Epstein-Barr virus

We have determined the sequence of herpes simplex virus type 1 DNA around the previously mapped location of sequences encoding an epitope of glycoprotein gH, and have deduced the structure of the gH gene and the amino acid sequence of gH. The unprocessed polypeptide is predicted to contain 838 amino acids, and to possess an N-terminal signal sequence and a C-terminal transmembrane sequence. Temperature-sensitive mutant tsQ26 maps within the predicted gH coding sequence. Homologous genes were identified in the genomes of two other herpesviruses, namely varicella-zoster virus and Epstein-Barr virus.

CAT vectors for analysis of eukaryotic promoters and enhancers

We have constructed two sets of plasmids for analysis of factors affecting mammalian gene expression. The pOCAT series contains a bacterial chloramphenicol-resistance expression unit (cat) and no eukaryotic promoter. The pUTKAT series contains the same cat unit under the control of the thymidine-kinase promoter of Herpes simplex virus. These plasmids are designed for testing effects of inserted regulatory elements on cat expression after transient transfection of mammalian cells in culture. We demonstrate here that the pOCAT series is useful for studying activities of inserted eukaryotic promoters, and the pUTKAT series is useful for studying activities of inserted eukaryotic enhancers.

Accumulation of herpes simplex virus type 1 RNAs of different kinetic classes in the cytoplasm of infected cells

We have analyzed the accumulation of herpes simplex virus type 1 RNA of the immediate early (IE; infected cell polypeptide types 4 and 0 [ICP-4 and ICP-0]), early (thymidine kinase), and early late (ICP-5) kinetic classes in the cytoplasm of infected cells in the presence of anisomycin, canavanine, or phosphonoacetic acid and in the course of a normal infection. IE RNAs were overproduced and were the only class of transcript detected in anisomycin-blocked cells. Phosphonoacetic acid treatment resulted in overaccumulation of early RNAs and underaccumulation of early late RNAs. Although low-stringency canavanine treatment resulted in accumulation of RNA from all kinetic classes, high-stringency conditions restricted accumulation of herpes simplex virus type 1 RNAs to the IE class. More importantly, the IE RNAs for ICP-4 and ICP-0 accumulated to a lesser extent under high-stringency canavanine conditions compared with their accumulation in anisomycin-treated cells. Therefore, the absence of newly synthesized viral proteins (anisomysin treatment) and the presence of analog proteins (stringent canavanine treatment) have different consequences with regard to the accumulation of these two IE RNAs. The kinetics of cytoplasmic accumulation for these RNAs was different for each class of RNA. The IE RNAs were detectable at 1 h postinfection and reached a maximum accumulation at ca. 3 h postinfection. The IE RNAs for both ICP-4 and ICP-0 persisted at late times of infection; however, they differed in that the RNA for ICP-4 remained at relatively low levels and the RNA for ICP-0 remained at relatively high levels as compared with their peak levels of accumulation. The 1.4-kilobase RNA for the herpes simplex virus type 1 thymidine kinase was detected by 2 h, with maximum accumulation occurring at ca. 5 h postinfection. After the peak of accumulation, the amount of thymidine kinase RNA declined rapidly from 8 to 14 h postinfection. The early late RNA for ICP-5 was detected between 2 and 3 h, after which accumulation increased to a peak between 8 and 10 h postinfection. The level of ICP-5 RNA remained at close to the peak level until 14 h postinfection. We also compared the accumulation of viral mRNAs in the cytoplasm with the rates of synthesis of their respective polypeptides. Our results suggest that translational controls may be involved in the regulation of IE genes but not early or late genes.

In vitro and in vivo transcription initiation sites on the TK-encoding BamHI Q fragment of HSV-1 DNA

The sites of in vitro transcription initiation on the BamHI Q fragment of herpes simplex virus DNA have been compared with the sites of 5' ends of RNAs made in vivo after virus infection. S1-nuclease protection analysis of these RNAs shows that there are in vivo counterparts for each of the five previously identified in vitro transcripts. The whole-cell-extract RNA polymerase II transcription system faithfully initiates RNAs predominantly at bona fide in vivo start sites and gives few, if any, false positive start sites. Further, antiparallel, self-complementary transcripts from the BamHI Q fragment were observed in the coding region of the HSV thymidine kinase gene.

Effects of orientation and position on the activity of a herpes simplex virus immediate early gene far-upstream region

It has previously been shown that a far-upstream region of the herpes simplex virus immediate early (IE) gene 3 increases the expression of a linked thymidine kinase (TK) gene and also contains sequences which respond to stimulation of transcription by a virion component. The effects of altering the orientation and distance of the far-upstream region with respect to the normal IE gene 3 promoter are described. Reversal of the orientation whilst retaining the normal position of the far-upstream region did not affect its activity, but placing it downstream from the TK gene abolished any detectable effect. When the far-upstream region was separated from the promoter by insertion of Escherichia coli DNA fragments (approximately 1000 base pairs), its activity was reduced but not prevented. A similar effect was observed for unstimulated expression of TK and stimulated expression in the presence of the virion component. The IE gene 3 far-upstream region therefore resembles enhancer sequences in some respects but also shows significant differences.

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.

Nucleotide sequence of the marmoset herpesvirus thymidine kinase gene and predicted amino acid sequence of thymidine kinase polypeptide

The nucleotide sequence of a 2549-bp DNA fragment containing the entire coding region of the marmoset herpesvirus (MarHV) thymidine kinase gene (tk) and the flanking sequences was determined by the dideoxynucleotide chain termination method. The MarHV thymidine kinase polypeptide predicted from the nucleotide sequence contained 376 amino acids and had a molecular weight of 41,281. The sequencing data also reveal that the coding portion of another MarHV gene probably begins only 292 nucleotides downstream from the stop codon of the MarHV tk gene. There was relatively little nucleotide sequence homology between the MarHV tk gene and that of the herpes simplex virus (HSV) types 1 and 2 tk genes. Comparisons of the predicted amino acid sequences of the MarHV thymidine kinase polypeptide with that of the HSV-1 and HSV-2 thymidine kinase polypeptides, however, revealed clear, but interrupted, homology within several regions of the polypeptide chains. Amino acid sequence homology was particularly striking at residues 10 to 27 of the MarHV thymidine kinase polypeptide and residues 49 to 66 of the HSV-1 and HSV-2 thymidine kinase polypeptides. These same amino acid residues exhibit noticeable sequence homology to the mitochondrial beta subunit ATPase, oncogene p21 protein, adenylate kinase, and to other nucleotide-binding proteins. It has been proposed that the indicated regions of homology are elements of a nucleotide-binding pocket in ATPase, p21, and adenylate kinase, raising the possibility that amino acid residues 15 to 25 of the MarHV thymidine kinase and 54 to 64 of the HSV-1 and HSV-2 enzymes are likewise parts of nucleotide-binding sites.

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.

A pattern of partially homologous recombination in mouse L cells

Herpes simplex virus thymidine kinase gene and pBR322 DNA (in large excess to the thymidine kinase gene) were introduced into mouse L cells by calcium phosphate DNA-mediated gene transfer. DNA fragments encompassing six junctions between the exogenous DNAs have been cloned and their nucleotide sequences determined. Analysis of these sequences has shown that stretches of partial homology involving from 20-50 base pairs are present near the points at which joining occurs between the donor molecules. The structure of the junction sequences suggests that the recombination event involves the alignment of the two donor DNA molecules at partially homologous regions followed by staggered cutting and joining. One donor molecule is always cut in the region of partial homology, while the second is cut at some distance that is a small multiple of 13.5 +/- 0.5 base pairs away (at 0, 14, 27, 39, 41, and 54 base pairs). In the three junctions where the second cut is far from the region of homology, a 17- to 19-base-pair segment of DNA separates the donor sequences. In all cases the origin of this "filler" DNA appears to be oligonucleotides derived from pBR322.

DNA fragments from F9 PyEC mutants increase expression of heterologous genes in transfected F9 cells

Restrictions fragments encompassing the DNA sequence changes, which allow polyoma mutants to productively infect embryonal carcinoma (EC) cells, have been coupled to the Herpes simplex virus thymidine kinase (HSV TK) gene and to the bacterial chloramphenicol acetyl transferase (CAT) gene. F9 TK(-) EC cells have been transfected with the TK constructions and transformation to TK(+) colonies has been determined. F9 EC cells, retinoic-acid-induced differentiating F9 cultures, mouse fibroblasts, and mouse myoblasts have been transfected with the CAT constructions and CAT enzyme activity has been measured from the transfected cells. The results suggest that the mutant changes function at the level of gene-expression enhancement, the mutant constructions increasing the TK transformation frequency and also yielding a higher level of CAT enzyme activity when compared with constructions having no polyoma fragment or the analogous wild-type polyoma restriction fragment. The sequence specificity for enhancement changes upon differentiation of F9 EC cells, with the CAT enzyme levels from the wild-type construction approaching the values obtained from a PyEC mutant construction having a single base-pair difference.

Genetic analysis of temperature-sensitive mutants of HSV-1: the combined use of complementation and physical mapping for cistron assignment

To date, mutations in mutants representing 19 of the 33 recognized HSV-1 complementation groups have been mapped. The physical map locations of mutations in 10 ts mutants of HSV-1 strain KOS representing 8 of the 19 complementation groups are reported herein. The mutations in three mutants were found to lie between coordinates 0.086 and 0.194--two of these were mapped finely to between coordinates 0.095 and 0.108--and in seven mutants, between 0.301 and 0.448. The mutation in 1 of the 10 mutants, tsQ26, was mapped finely to a sequence between 500 and 1000 base pairs to the left of the 3' end of the TK gene (0.301-0.304). The availability of physical mapping data has (1) confirmed the usefulness of the complementation test as a means of identifying viral gene functions, (2) facilitated the rapid assignment of mutants to new and recognized cistrons, and (3) prompted a reevaluation of previously ambiguous complementation for mutants in 2 complementation groups. Thus, the 10 mutants whose ts mutations were mapped in this study had been assigned previously to 8 complementation groups based on the assumption that complementation indices of 2 or greater signified that 2 mutants were in different genes. Combined with physical mapping data, however, the results of complementation tests now indicate that indices between 2 and 10 may reflect either inter- or intragenic complementation. Thus, the 10 mutants have now been assigned to 7 complementation groups. Although physical mapping data have confirmed the results of previous complementation tests for 6 of 8 groups analyzed, reevaluation of complementation data in the light of physical mapping data has resulted in a more precise genetic definition of the locus for viral DNA polymerase and of a locus (represented by mutants in complementation group 1-10) which maps in the left hand portion of UL.

The autonomous parvovirus MVM encodes two nonstructural proteins in addition to its capsid polypeptides

In vitro translation of mRNA from cells infected with the autonomous parvovirus MVM yields four major virally coded proteins. Two of these proteins are indistinguishable both antigenically and by peptide map analysis from the viral capsid polypeptides VP-1 and VP-2. The other two proteins, designated NS-1 and NS-2, are not related to the capsid polypeptides but are recognized by sera from animals infected with different autonomous parvovirus serotypes. The NS-1 protein made in vitro comigrates with VP-1 (MW approximately 83,000), while the NS-2 polypeptide has an apparent molecular weight of 24,000. The transcript for the NS-1 polypeptide was mapped to a block of open reading frame located in the major intron of the left-hand transcription unit in the MVM genome.

Nucleotide sequence of the herpes simplex virus type 2 thymidine kinase gene

We have determined the complete nucleotide sequence of the thymidine kinase gene of herpes simplex virus (HSV) type 2 strain 333. The sequence of the thymidine kinase gene exhibits an open translational reading frame of 1,128 nucleotides encoding a protein of 376 amino acids. The DNA sequence was compared with that of the HSV type 1 thymidine kinase gene from strain MP (S. L. McKnight, Nucleic Acids Res. 8:5949-5964, 1980) and from strain CL 101 (M. J. Wagner, J. A. Sharp, and W. C. Summers, Proc. Natl. Acad. Sci. U.S.A. 78:1441-1445, 1981) to assess the extent of intra- and intertypic variation for one viral gene. The nucleotides encoding the structural gene varied 1.7% between the two HSV type 1 strains and 19% between HSV type 1 and HSV type 2, which translated to differences in the amino acid sequence of the two proteins of 1.9 and 27%, respectively. The DNA encoding the 5' regulatory sequences appeared to be more conserved than the DNA coding for the structural gene, and the DNA at the 3' end of the gene was the least homologous.