Physical mapping of herpes simplex virus type 1 ts mutants by marker rescue: correlation of the physical and genetic maps

Phylogenetic and Genomic Characterization of Whole Genome Sequences of Ocular Herpes Simplex Virus Type 1 Isolates Identifies Possible Virulence Determinants in Humans

Purpose

There are limited data on the prevalence and genetic diversity of herpes simplex virus type 1 (HSV-1) virulence genes in ocular isolates. Here, we sequenced 36 HSV-1 ocular isolates, collected by the Bascom Palmer Eye Institute, a university-based eye hospital, from three different ocular anatomical sites (conjunctiva, cornea, and eyelid) and carried out a genomic and phylogenetic analyses.

Methods

The PacBio Sequel II long read platform was used for genome sequencing. Phylogenetic analysis and genomic analysis were performed to help better understand genetic variability among common virulence genes in ocular herpetic disease.

Results

A phylogenetic network generated using the genome sequences of the 36 Bascom Palmer ocular isolates, plus 174 additional strains showed that ocular isolates do not group together phylogenetically. Analysis of the thymidine kinase and DNA polymerase protein sequences from the Bascom Palmer isolates showed multiple novel single nucleotide polymorphisms, but only one, BP-K14 encoded a known thymidine kinase acyclovir resistance mutation. An analysis of the multiple sequence alignment comprising the 51 total ocular isolates versus 159 nonocular strains detected several possible single nucleotide polymorphisms in HSV-1 genes that were found significantly more often in the ocular isolates. These genes included UL6, gM, VP19c, VHS, gC, VP11/12, and gG.

Conclusions

There does not seem to be a specific genetic feature of viruses causing ocular infection. The identification of novel and common recurrent polymorphisms may help to understand the drivers of herpetic pathogenicity and specific factors that may influence the virulence of ocular disease.

Penciclovir-Resistance Mutations in the Herpes Simplex Virus DNA Polymerase Gene

Penciclovir is the active form of the orally available prodrug famciclovir, which is entering clinical use for herpesvirus infections. Like aciclovir, penciclovir is an acyclic guanosine analogue that is phosphorylated by viral thymidine kinase and whose triphosphate can inhibit viral DNA polymerase. We tested several well-characterized herpes simplex virus mutants with aciclovir-resistance mutations in the viral DNA polymerase gene for altered sensitivity to penciclovir. The mutants varied in their susceptibilities to penciclovir with one exhibiting 2-fold hypersensitivity, one marginal resistance and three about 3-fold resistance. Marker rescue and DNA sequencing analyses mapped the penciclovir-resistance mutation of one mutant, AraA r7, to a single base change that alters a glycine to a cysteine at residue 841 within conserved region III of α-like DNA polymerases. The results have implications for the mechanism of selective action of penciclovir, for the potential for development of resistance in the clinic, and for the substrate recognition properties of herpes simplex virus DNA polymerase.

Recombination Analysis of Herpes Simplex Virus 1 Reveals a Bias toward GC Content and the Inverted Repeat Regions

Herpes simplex virus 1 (HSV-1) causes recurrent mucocutaneous ulcers and is the leading cause of infectious blindness and sporadic encephalitis in the United States. HSV-1 has been shown to be highly recombinogenic; however, to date, there has been no genome-wide analysis of recombination. To address this, we generated 40 HSV-1 recombinants derived from two parental strains, OD4 and CJ994. The 40 OD4-CJ994 HSV-1 recombinants were sequenced using the Illumina sequencing system, and recombination breakpoints were determined for each of the recombinants using the Bootscan program. Breakpoints occurring in the terminal inverted repeats were excluded from analysis to prevent double counting, resulting in a total of 272 breakpoints in the data set. By placing windows around the 272 breakpoints followed by Monte Carlo analysis comparing actual data to simulated data, we identified a recombination bias toward both high GC content and intergenic regions. A Monte Carlo analysis also suggested that recombination did not appear to be responsible for the generation of the spontaneous nucleotide mutations detected following sequencing. Additionally, kernel density estimation analysis across the genome found that the large, inverted repeats comprise a recombination hot spot.

IMPORTANCE

Herpes simplex virus 1 (HSV-1) virus is the leading cause of sporadic encephalitis and blinding keratitis in developed countries. HSV-1 has been shown to be highly recombinogenic, and recombination itself appears to be a significant component of genome replication. To date, there has been no genome-wide analysis of recombination. Here we present the findings of the first genome-wide study of recombination performed by generating and sequencing 40 HSV-1 recombinants derived from the OD4 and CJ994 parental strains, followed by bioinformatics analysis. Recombination breakpoints were determined, yielding 272 breakpoints in the full data set. Kernel density analysis determined that the large inverted repeats constitute a recombination hot spot. Additionally, Monte Carlo analyses found biases toward high GC content and intergenic and repetitive regions.

Mechanisms by which herpes simplex virus DNA polymerase limits translesion synthesis through abasic sites

Results suggest a high probability that abasic (AP) sites occur at least once per herpes simplex virus type 1 (HSV-1) genome. The parameters that control the ability of HSV-1 DNA polymerase (pol) to engage in AP translesion synthesis (TLS) were examined because AP lesions could influence the completion and fidelity of viral DNA synthesis. Pre-steady-state kinetic experiments demonstrated that wildtype (WT) and exonuclease-deficient (exo-) pol could incorporate opposite an AP lesion, but full TLS required absence of exo function. Virtually all of the WT pol was bound at the exo site to AP-containing primer-templates (P/Ts) at equilibrium, and the pre-steady-state rate of excision by WT pol was higher on AP-containing than on matched DNA. However, several factors influencing polymerization work synergistically with exo activity to prevent HSV-1 pol from engaging in TLS. Although the pre-steady-state catalytic rate constant for insertion of dATP opposite a T or AP site was similar, ground-state-binding affinity of dATP for insertion opposite an AP site was reduced 3-9-fold. Single-turnover running-start experiments demonstrated a reduced proportion of P/Ts extended to the AP site compared to the preceding site during processive synthesis by WT or exo- pol. Only the exo- pol engaged in TLS, though inefficiently and without burst kinetics, suggesting a much slower rate-limiting step for extension beyond the AP site.

Susceptibility of drug-resistant clinical herpes simplex virus type 1 strains to essential oils of ginger, thyme, hyssop, and sandalwood

Acyclovir-resistant clinical isolates of herpes simplex virus type 1 (HSV-1) were analyzed in vitro for their susceptibilities to essential oils of ginger, thyme, hyssop, and sandalwood. All essential oils exhibited high levels of virucidal activity against acyclovir-sensitive strain KOS and acyclovir-resistant HSV-1 clinical isolates and reduced plaque formation significantly.

Antibacterial, antiviral, antiproliferative and apoptosis-inducing properties of Brackenridgea zanguebarica (Ochnaceae)

Brackenridgea zanguebarica is a small tree that is used in traditional African medicine as a type of cure-all for many diseases, including the treatment of wounds. The yellow bark of B. zanguebarica was used for the preparation of an ethanolic extract, which was tested in various concentrations against eleven bacteria, Herpes simplex virus type 1 (HSV-1) and different human tumour cell lines. The extract that contains different polyphenolic substances like calodenin B. Cell growth inhibition, assessed via MTT-assay, was found in all tested human cell lines with IC50 values (concentration of extract that reduced cell viability by 50%) between 33 microg dry extract/mL for HL-60 human myeloid leukaemia cells and 93 microg dry extract/mL for HaCaT human keratinocytes. Staining with Annexin-V-FLUOS and JC-1 followed by subsequent analysis via flow cytometry revealed significant apoptosis-inducing properties. Analysis of caspase activity using a fluorogenic caspase-3 substrate showed a significant caspase activity in Jurkat T-cells after incubation with the extract. The bark extract had a pronounced activity against free HSV-1 and a strong antibacterial activity against Gram-positive strains (MICs: 6-24 microg dry extract/mL), which are often involved in skin infections. Additionally, no irritating properties of the extract could be observed in hen-egg test chorioallantoic membrane (HET-CAM) assay. These findings give a rationale for the traditional use of B. zanguebarica and are a basis for further analysis of the plant's components, their biological activity, and its use in modern phytotherapy.

Virucidal activity of a GT-rich oligonucleotide against herpes simplex virus mediated by glycoprotein B

We have investigated the antiviral mechanism of a phosphorothioate oligonucleotide, ISIS 5652, which has activity against herpes simplex virus (HSV) in the low micromolar range in plaque reduction assays. We isolated a mutant that is resistant to this compound. Marker rescue and sequencing experiments showed that resistance was due to at least one of three mutations in the UL27 gene which result in amino acid changes in glycoprotein B (gB). Because gB has a role in attachment and entry of HSV, we tested the effects of ISIS 5652 at these stages of infection. The oligonucleotide potently inhibited attachment of virus to cells at 4 degrees C; however, the resistant mutant did not exhibit resistance at this stage. Moreover, a different oligonucleotide with little activity in plaque reduction assays was as potent as ISIS 5652 in inhibiting attachment. Similarly, ISIS 5652 was able to inhibit entry of pre-attached virions into cells at 37 degrees C, but the mutant did not exhibit resistance in this assay. The mutant did not attach to or enter cells more quickly than did wild-type virus. Strikingly, incubation of wild-type virus with 1 to 2 microM ISIS 5652 at 37 degrees C led to a time-dependent, irreversible loss of infectivity (virucidal activity). No virucidal activity was detected at 4 degrees C or with an unrelated oligonucleotide at 37 degrees C. The resistant mutant and a marker-rescued derivative containing its gB mutations exhibited substantial resistance to this virucidal activity of ISIS 5652. We hypothesize that the GT-rich oligonucleotide induces a conformational change in gB that results in inactivation of infectivity.

Virucidal effect of peppermint oil on the enveloped viruses herpes simplex virus type 1 and type 2 in vitro

The virucidal effect of peppermint oil, the essential oil of Mentha piperita, against herpes simplex virus was examined. The inhibitory activity against herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) was tested in vitro on RC-37 cells using a plaque reduction assay. The 50% inhibitory concentration (IC50) of peppermint oil for herpes simplex virus plaque formation was determined at 0.002% and 0.0008% for HSV-1 and HSV-2, respectively. Peppermint oil exhibited high levels of virucidal activity against HSV-1 and HSV-2 in viral suspension tests. At noncytotoxic concentrations of the oil, plaque formation was significantly reduced by 82% and 92% for HSV-1 and HSV-2, respectively. Higher concentrations of peppermint oil reduced viral titers of both herpesviruses by more than 90%. A clearly time-dependent activity could be demonstrated, after 3 h of incubation of herpes simplex virus with peppermint oil an antiviral activity of about 99% could be demonstrated. In order to determine the mode of antiviral action of the essential oil, peppermint oil was added at different times to the cells or viruses during infection. Both herpesviruses were significantly inhibited when herpes simplex virus was pretreated with the essential oil prior to adsorption. These results indicate that peppermint oil affected the virus before adsorption, but not after penetration into the host cell. Thus this essential oil is capable to exert a direct virucidal effect on HSV. Peppermint oil is also active against an acyclovir resistant strain of HSV-1 (HSV-1-ACV(res)), plaque formation was significantly reduced by 99%. Considering the lipophilic nature of the oil which enables it to penetrate the skin, peppermint oil might be suitable for topical therapeutic use as virucidal agent in recurrent herpes infection.

ICP0 is required for efficient reactivation of herpes simplex virus type 1 from neuronal latency

Relative to wild-type herpes simplex virus type 1 (HSV-1), ICP0-null mutant viruses reactivate inefficiently from explanted, latently infected mouse trigeminal ganglia (TG), indicating that ICP0 is not essential for reactivation but plays a central role in enhancing the efficiency of reactivation. The validity of these findings has been questioned, however, because the replication of ICP0-null mutants is impaired in animal models during the establishment of latency, such that fewer mutant genomes than wild-type genomes are present in latently infected mouse TG. Therefore, the reduced number of mutant viral genomes available to reactivate, rather than mutations in the ICP0 gene per se, may be responsible for the reduced reactivation efficiency of ICP0-null mutants. We have recently demonstrated that optimization of the size of the ICP0 mutant virus inoculum and transient immunosuppression of mutant-infected mice with cyclophosphamide can be used to establish wild-type levels of ICP0-null mutant genomes in latently infected TG (W. P. Halford and P. A. Schaffer, J. Virol. 74:5957-5967, 2000). Using this procedure to equalize mutant and wild-type genome numbers, the goal of the present study was to determine if, relative to wild-type virus, the absence of ICP0 function in two ICP0-null mutants, n212 and 7134, affects reactivation efficiency from (i) explants of latently infected TG and (ii) primary cultures of latently infected TG cells. Although equivalent numbers of viral genomes were present in TG of mice latently infected with either wild-type or mutant viruses, reactivation of n212 and 7134 from heat-stressed TG explants was inefficient (31 and 37% reactivation, respectively) relative to reactivation of wild-type virus (KOS) (95%). Similarly, n212 and 7134 reactivated inefficiently from primary cultures of dissociated TG cells plated directly after removal from the mouse (7 and 4% reactivation, respectively), relative to KOS (60% reactivation). The efficiency and kinetics of reactivation of KOS, n212, and 7134 from cultured TG cells (treated with acyclovir to facilitate the establishment of latency) in response to heat stress or superinfection with a nonreplicating HSV-1 ICP4(-) mutant, n12, were compared. Whereas heat stress induced reactivation of KOS from 69% of latently infected TG cell cultures, reactivation of n212 and 7134 was detected in only 1 and 7% of cultures, respectively. In contrast, superinfection with the ICP4(-) virus, which expresses high levels of ICP0, resulted in the production of infectious virus in nearly 100% of cultures latently infected with KOS, n212, or 7134 within 72 h. Thus, although latent mutant viral genome loads were equivalent to that of wild-type virus, in the absence of ICP0, n212 and 7134 reactivated inefficiently from latently infected TG cells during culture establishment and following heat stress. Collectively, these findings demonstrate that ICP0 is required to induce efficient reactivation of HSV-1 from neuronal latency.

Mechanism and application of genetic recombination in herpesviruses

Herpes simplex virus type 1 (HSV-1) is a ubiquitous human pathogen that latently infects sensory ganglia and encodes over 80 genes in a 152 kbp DNA genome. This well characterised virus provides a model for analysing genetic recombination in herpesviruses, a fundamental biological process by which new combinations of genetic materials are generated. The frequency of homologous recombination was estimated to be 0.0048-0.007 (0.48%-0.7%)/kb of the HSV-1 genome, determined using physical markers. The double-strand break repair model, the current model of homologous recombination, adequately explains L-S inversion of herpesvirus genomes and the recombinogenicity of the a sequence. Several herpesvirus genomes, including HSV-1 consist of a unique sequence bracketed by a pair of inverted repeat sequences. This arrangement is attributed to illegitimate recombination between molecules arranged in an inverse orientation. Junctions of unique and repeated sequences that correspond to the crossover site of illegitimate recombination are recombinogenic. Recombination is important for virus evolution, construction of mutated virus, gene therapy and vaccination in which the potential for recombination between engineered input virus and wild type virus has to be considered.

Herpes simplex virus DNA replication

The Herpesviridae comprise a large class of animal viruses of considerable public health importance. Of the Herpesviridae, replication of herpes simplex virustype-1 (HSV-1) has been the most extensively studied. The linear 152-kbp HSV-1 genome contains three origins of DNA replication and approximately 75 open-reading frames. Of these frames, seven encode proteins that are required for originspecific DNA replication. These proteins include a processive heterodimeric DNA polymerase, a single-strand DNA-binding protein, a heterotrimeric primosome with 5'-3' DNA helicase and primase activities, and an origin-binding protein with 3'-5' DNA helicase activity. HSV-1 also encodes a set of enzymes involved in nucleotide metabolism that are not required for viral replication in cultured cells. These enzymes include a deoxyuridine triphosphatase, a ribonucleotide reductase, a thymidine kinase, an alkaline endo-exonuclease, and a uracil-DNA glycosylase. Host enzymes, notably DNA polymerase alpha-primase, DNA ligase I, and topoisomerase II, are probably also required. Following circularization of the linear viral genome, DNA replication very likely proceeds in two phases: an initial phase of theta replication, initiated at one or more of the origins, followed by a rolling-circle mode of replication. The latter generates concatemers that are cleaved and packaged into infectious viral particles. The rolling-circle phase of HSV-1 DNA replication has been reconstituted in vitro by a complex containing several of the HSV-1 encoded DNA replication enzymes. Reconstitution of the theta phase has thus far eluded workers in the field and remains a challenge for the future.

Herpes simplex virus type 1 DNA replication is specifically required for high-frequency homologous recombination between repeated sequences

Using an assay for recombination that measures deletion of a beta-galactosidase gene positioned between two directly repeated 350-bp sequences in plasmids transiently maintained in COS cells, we have found that replication from a simian virus 40 origin produces a high frequency of nonhomologous recombination. In contrast, plasmids replicating from a herpesvirus origin (oris) in COS cells superinfected with herpes simplex virus type 1 (HSV-1) show high levels of homologous recombination between the repeats and an enhanced recombinogenicity of the HSV-1 a sequence that is not seen during simian virus 40 replication. When the same assay was used to study recombination between 120- to 150-bp repeats in uninfected Vero cells, the level of recombination was extremely low or undetectable (< 0.03%), consistent with the fact that these repeats are smaller than the minimal efficient processing sequence for homologous recombination in mammalian cells. Recombination between these short repeats was easily measurable (0.5 to 0.8%) following HSV-1 infection, suggesting that there is an alteration of the recombination machinery. The frequency of recombination between repeats of the Uc-DR1 region, previously identified as the only segment of the HSV-1 a sequence indispensable for enhanced a-sequence recombination, was not significantly higher than that measured for other short sequences.

Rapid small-scale isolation of herpes simplex virus DNA

A method has been developed for the rapid isolation of herpes simplex virus DNA analogous to miniprep methods for bacterial plasmid isolation. Infected Vero cells are lysed with three freeze-thaw cycles, and the nuclei are removed by centrifugation. DNA is released from the virions in the supernatant by proteinase K digestion. Then the DNA is extracted with phenol/chloroform and precipitated with ethanol. This method requires only small amounts of infected cells as a source of viral DNA, does not use radioactivity, and routinely produces DNA of sufficient purity to be used for restriction fragment length polymorphism (RFLP) analysis on ethidium-stained gels.

Substitution of a TATA box from a herpes simplex virus late gene in the viral thymidine kinase promoter alters ICP4 inducibility but not temporal expression

The role of cis-acting promoter elements associated with herpes simplex virus type 1 (HSV-1) early and late genes was evaluated during productive infection with regard to activation of gene expression by the HSV-1 transactivator ICP4 and control of temporal regulation. A set of recombinant viruses was constructed such that expression of an HSV-1 early gene, thymidine kinase (tk), was placed under the control of either the tk TATA box or the TATA box from the late gene, glycoprotein C (gC), in the presence or absence of the upstream Sp1 and CCAAT sites normally found in the tk promoter. The presence of Sp1 sites in the promoter or replacement of the tk TATA box with the gC TATA box resulted in a decreased activation of tk mRNA expression by ICP4. Substitution of the A + T-rich region from the gC TATA box in the context of the remainder of the surrounding tk sequences resulted in a promoter that bound recombinant TATA-binding protein (TBP) better at lower concentrations than the wild-type tk promoter did. These results indicate that tk promoters that are better able to utilize TBP are less responsive to ICP4 activation and suggest that activation by ICP4 involves the general transcription factors that interact with TBP or TBP itself. Additionally, all of the viruses expressed tk at early times postinfection, indicating that cis-acting promoter elements that control the level of expression of HSV-1 early and late genes do not determine temporal regulation.

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.

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.

Aphidicolin resistance in herpes simplex virus type I reveals features of the DNA polymerase dNTP binding site

We describe the mapping and sequencing of mutations within the DNA polymerase gene of herpes simplex virus type 1 which confer resistance to aphidicolin, a DNA polymerase inhibitor. The mutations occur near two regions which are highly conserved among DNA polymerases related to the herpes simplex enzyme. They also occur near other herpes simplex mutations which affect the interactions between the polymerase and deoxyribonucleoside triphosphate substrates. Consequently, we argue in favor of the idea that the aphidicolin binding site overlaps the substrate binding site and that the near-by conserved regions are functionally required for substrate binding. Our mutants also exhibit abnormal sensitivity to another DNA polymerase inhibitor, phosphonoacetic acid. This drug is thought to bind as an analogue of pyrophosphate. A second-site mutation which suppresses the hypersensitivity of one mutant to phosphonoacetic acid (but not its aphidicolin resistance) is described. This second mutation may represent a new class of mutations, which specifically affects pyrophosphate, but not substrate, binding.

Localization of a herpes simplex virus neurovirulence gene dissociated from high-titer virus replication in the brain

Previous studies with the herpes simplex virus type 1 X type 2 intertypic recombinant RS6 suggested that the genomic region from 0.11 to 0.14 map units is involved in neurovirulence (R. T. Javier, R. L. Thompson, and J. G. Stevens, J. Virol. 61:1978-1984, 1987). To study this further, we isolated an RS6-derived herpes simplex virus intertypic recombinant (R13-1) which has a genetic defect within this area. After inoculation into mouse brains, R13-1 was found to be approximately 10,000-fold less neurovirulent than either the wild-type type 1 or type 2 parental virus. However, R13-1 replicated in the mouse brain to titers resembling those of the wild-type parents. Further comparisons with wild-type counterparts indicated that R13-1 expressed equivalent levels of the enzyme thymidine kinase and replicated to intermediate levels in primary mouse embryo fibroblasts maintained at the normal body temperature for mice. Using marker rescue techniques combined with in vivo selection, we found that recombination between unit-length R13-1 DNA and a cloned type 1 DNA fragment spanning the region from 0.11 to 0.14 map units (EcoRI-d, 0.079 to 0.192 map units) generated viruses with a wild-type neurovirulence phenotype. To further refine the genomic region of interest, we performed marker rescue experiments using two EcoRI-d subclones, EcoRI/BamHI dc (0.079 to 0.143 map units) and BamHI/EcoRI and (0.143 to 0.192 map units), representing the left and right halves of the EcoRI d fragment, respectively. In these experiments the EcoRI/BamHI dc clone, but not the BamHI/EcoRI ad clone, yielded recombinant viruses exhibiting wild-type neurovirulence. These results show that at least one herpes simplex virus gene function associated with neurovirulence is located within a 9.1-kilobase region at 0.079 to 0.143 map units of the viral genome. Perhaps more significantly, the results indicate that this neurovirulence property functions independently of high-titer virus replication in the brain.

A temperature-sensitive mutation in a herpes simplex virus type 1 gene required for viral DNA synthesis maps to coordinates 0.609 through 0.614 in UL

ts701 is a temperature-sensitive mutant of herpes simplex virus type 1 strain KOS induced by hydroxylamine mutagenesis (C.T. Chu, D. S. Parris, R. A. F. Dixon, F. E. Farber, and P. A. Schaffer, Virology 98:168-181, 1979). In the present study, the mutation rendering ts701 temperature sensitive was mapped to coordinates 0.609 through 0.614 in the UL region of the genome. At the nonpermissive temperature, ts701 (i) failed to induce the synthesis of viral DNA, (ii) exhibited a dramatically reduced ability to drive replication of a plasmid containing the herpes simplex virus origin of viral DNA synthesis, oriS, (iii) generated no viral polypeptides of the late (gamma 2) kinetic class, and (iv) produced virions with electron-translucent cores. Northern (RNA) blot hybridization demonstrated that two mRNAs--one of the beta kinetic class and one of the gamma kinetic class--hybridized to a 1.3-kilobase viral DNA fragment that rescued the mutation in ts701. Based on the phenotype and mapping of ts701, it is likely that its mutation lies in the gene specifying the 65,000-Mr DNA-binding protein (65KDBP) recently described by Marsden et al. (H.S. Marsden, M.E.M. Campbell, L. Haarr, M. C. Frame, D. S. Parris, M. Murphy, R. G. Hope, M. T. Muller, and C. M. Preston, J. Virol. 61:2428-2437, 1987).

Isolation and characterization of herpes simplex virus type 1 host range mutants defective in viral DNA synthesis

Cell lines were generated by cotransfection of Vero cells with pSV2neo and a plasmid containing the herpes simplex virus type 1 (HSV-1) EcoRI D fragment (coordinates 0.086 to 0.194). One such cell line (S22) contained the genes for alkaline exonuclease and several uncharacterized functions. Three mutant isolates of HSV-1 strain KOS which grew on S22 cells but not on normal Vero cells were isolated and characterized. All three mutants (hr27, hr48, and hr156) were defective in the synthesis of viral DNA and late proteins when grown in nonpermissive Vero cells. Early gene expression in cells infected with these host range mutants appeared to be normal at the nonpermissive condition. The mutations were mapped by marker rescue to a 1.5-kilobase fragment (coordinates 0.145 to 0.155). The mutation of one of these mutants, hr27, was more finely mapped to an 800-base-pair region (coordinates 0.145 to 0.151). This position of these mutations is consistent with the map location of a putative 94-kilodalton polypeptide as determined by sequence analysis (D. McGeoch, personal communication). Complementation studies demonstrated that these mutants formed a new complementation group, designated 1-36. The results presented in this report indicate that the 94-kilodalton gene product affected by these mutations may have a direct role in viral DNA synthesis.

Herpes simplex virus type 1-induced ribonucleotide reductase activity is dispensable for virus growth and DNA synthesis: isolation and characterization of an ICP6 lacZ insertion mutant

Herpes simplex virus (HSV) encodes a ribonucleotide reductase consisting of two subunits (140 and 38 kilodaltons) whose genes map to coordinates 0.56 to 0.60 on the viral genome. Host cell lines containing the HpaI F fragment which includes the reductase subunit genes of HSV type 1 strain KOS (coordinates 0.535 to 0.620) were generated. Transfection of these cells with a plasmid containing the immediate-early ICP0 gene resulted in the expression of ICP6; interestingly, ICP4 plasmids failed to induce expression, indicating an unusual pattern of ICP6 regulation. One such cell line (D14) was used to isolate a mutant with the structural gene of lacZ inserted into the ICP6 gene such that the lacZ gene is read in frame with the N-terminal region of ICP6. This mutant generated a protein containing 434 amino acids (38%) of the N terminus of ICP6 fused to beta-galactosidase under control of the endogenous ICP6 promoter. Screening for virus recombinants was greatly facilitated by staining virus plaques with 5-bromo-4-chloro-3-indoyl-beta-D-galactoside (X-gal). Enzyme assays of infected BHK cells indicated that the mutant is incapable of inducing viral ribonucleotide reductase activity. Surprisingly, although plaque size was greatly reduced, mutant virus yield was reduced only four- to fivefold compared with that of the wild type grown in exponentially growing Vero cells. Mutant virus plaque size, yields, and ability to synthesize viral DNA were more severely compromised in serum-starved cells as compared with the wild type grown under the same condition. Although our evidence suggests that the HSV type 1 ribonucleotide reductase is not required for virus growth and DNA replication in dividing cells, it may be required for growth in nondividing cells.

Establishment of latency in vitro with herpes simplex virus temperature-sensitive mutants at nonpermissive temperature

This report describes a latency model using human embryo lung cells that were infected with herpes simplex virus type 1 (HSV-1) temperature-sensitive (ts) mutants and cultivated at nonpermissive temperature (40.5 degrees C). ts mutants tsG8 (parental strain HSV-1 KOS) and tsG5 (parental strain HSV-1 13) could be maintained in a latent state at 40.5 degrees C for at least 40 days without exhibiting virus infectivity. During this time, viable virus could be reactivated by reducing the incubation temperature to the permissive level (34 degrees C). Virus replication could be detected 2 to 6 days after temperature reduction and the virus reactivated from the latent state seemed to retain the same ts phenotype as the input virus for at least 14 days.

Influencing of ionizing radiation on herpes simplex virus and its genome

The effects of cobalt-60 gamma-rays, 10 MeV electrons and 52 MeV deutrons on the survival of plaque-forming ability has been studied in various strains of herpes simplex virus (HSV). The results show that the D0 for the loss of plaque-forming ability in different HSV strains lies in the range 1-3 kGy. Irradiation of isolated HSV-1 DNA with cobalt-60 gamma-rays resulted in damage, as indicated by electrophoresis of purified viral DNA and by restriction endonuclease analysis, at doses of 1 kGy, with complete loss of structure at doses above 4 kGy. The infectivity of the irradiated naked DNA was lost at doses above 4 kGy, but after irradiation of the intact virus some plaque-forming ability was retained after doses of 10 or even 40 kGy. Thus the organization within the viral capsid may play a protective role by modifying the severity of the radiation damage, and preserving at least some degree of infectivity.

The effect of (E)-5-(2-bromovinyl)-2'-deoxyuridine on DNA repair and mutagenesis of herpes simplex virus type 1

Growth of HSV-1 in (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) results in incorporation of the analog into HSV-1 DNA. Employing the technique of Weigle-type reactivation (WR), HSV-1 inactivated by uv irradiation but not by growth in BVDU is a substrate for induced cellular repair pathways. Growth of mammalian cells in BVDU does not induce cellular repair pathways detected by WR. HSV-1 temperature sensitive (ts) mutants demonstrate an increased reversion frequency to the nonpermissive phenotype (ts+) following growth in a high concentration of BVDU. A ts mutant did not display an increased reversion frequency following growth in equally inhibitory concentrations of an HSV-1 polymerase inhibitor, aphidicolin. These findings suggest that BVDU incorporated into HSV-1 DNA may not be readily excised and may be a mutagenic lesion in viral DNA, although other explanations are possible.

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.

Activities of herpes simplex virus type 1 (HSV-1) ICP4 genes specifying nonsense peptides

Synthetic oligonucleotide linkers containing translational termination codons in all possible reading frames were inserted at various positions in the cloned gene encoding the herpes simplex virus type 1 (HSV-1) immediate-early regulatory protein, ICP4. It was determined that the amino-terminal 60 percent of the ICP4 gene was sufficient for trans-induction of a thymidine kinase promoter-CAT chimera (pTKCAT) and negative regulation of an ICP4 promoter-CAT chimera (pIE3CAT); however, it was relatively inefficient in complementing an ICP4 deletion mutant. The amino-terminal ninety amino acids do not appear to be required for infectivity as reflected by the replication competence of a mutant virus containing a linker insertion at amino acid 12. The size of the ICP4 molecule expressed from the mutant virus was consistent with translational restart at the next methionine codon corresponding to amino acid 90 of the deduced ICP4 amino acid sequence.

DNA processing in temperature-sensitive morphogenic mutants of HSV-1

The anatomy of DNA synthesized by five HSV-1 mutants previously shown to accumulate predominantly empty capsids at the nonpermissive temperature (NPT) was analyzed with Bg/II restriction digestion. At the NPT, all five generated DNA lacking termini, indicating that in the absence of packaging, viral DNA is not processed to unit length. One mutant, F18, was able to process DNA made at the NPT to unit length molecules during a 6-hr period after shift to the permissive temperature. The appearance of unit length molecules correlated with the appearance of staphylococcal nuclease-resistant F18 DNA.

Mutants defective in herpes simplex virus type 2 ICP4: isolation and preliminary characterization

Vero cells were biochemically transformed with the gene encoding ICP4 of herpes simplex virus type 2 (HSV-2). These cells were used as permissive hosts to isolate and propagate HSV-2 mutants defective in this gene. Two mutants, designated hr259 and hr79, were isolated. Neither mutant grew in nontransformed Vero cells, but both grew to near wild-type levels in HSV-2 ICP4-expressing cells. hr259 contains a deletion of about 0.6 kilobases which eliminates the mRNA start site of the ICP4 gene. hr79 contains a mutation which maps by marker rescue to the portion of the ICP4 gene encoding the carboxy-terminal half of the protein. Although hr259 failed to generate any detectable ICP4 mRNA in nontransformed Vero cells, hr79 encoded an ICP4 mRNA which is wild type with respect to size. In nontransformed Vero cells infected with hr259, only ICP0, ICP6, ICP22, and ICP27 were readily detectable. In the case of hr79, a truncated form of ICP4 appeared to be made in addition to ICP0, ICP6, ICP22, and ICP27. Both hr259 and hr79 grew efficiently on cell lines transformed with the ICP4 gene of HSV-1 as evidenced by plating efficiencies and single-burst experiments. Similarly, cells transformed with the ICP4 gene of HSV-2 served as efficient hosts for the growth of d120, HSV-1 ICP4 deletion mutant.

Effects of Bloom's syndrome fibroblasts on genetic recombination and mutagenesis of herpes simplex virus type 1

The effects of Bloom's syndrome (BS) fibroblasts on genetic recombination and the mutation frequency of herpes simplex virus type 1 (HSV-1) was determined by employing two factor crosses of selected temperature-sensitive (ts) mutants. A significant increase in the recombination frequency (RF) was observed in seven of nine crosses when multiple BS fibroblast lines were compared to normal human fibroblasts. The RF of HSV-1 ts mutants increased following 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment of normal, but not BS fibroblasts, suggesting that BS fibroblasts express higher constitutive levels of genetic recombination activity. HSV-1 ts mutants demonstrated significantly higher reversion frequencies to the nontemperature sensitive (ts+) phenotype following growth in BS rather than normal fibroblasts, indicating that exogenous viral DNA encoding many of the enzymes necessary for its own replication is affected by the mutator phenotype of BS.

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

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

Herpes simplex virus type 1 ICP27 is an essential regulatory protein

The five immediate-early genes of herpes simplex virus are expressed during the initial stages of the infectious cycle, and certain immediate-early proteins have been shown to play a regulatory role in subsequent viral gene expression. Until recently, the functional properties of only one immediate-early protein, ICP4, had been examined in any detail, primarily because mutants had been isolated only in the gene for ICP4. We report herein the genetic and phenotypic characterization of four temperature-sensitive mutants of herpes simplex virus type 1 (tsY46, tsE5, tsE6, and tsLG4) that have begun to elucidate the function(s) of a second immediate-early protein, ICP27. The four mutants complemented each other inefficiently or not at all, indicating that they are defective in the same function. Marker rescue tests placed the mutations in tsY46 and tsE5 in sequences that encode the transcript for ICP27; the mutations in tsE6 and tsLG4 lie in or near these sequences. The ability of wild-type ICP27 expressed from a cloned gene to complement tsY46 and tsLG4 constitutes additional evidence that these mutants are defective in an ICP27-associated function. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of mutant-infected cell polypeptides showed that certain immediate-early (alpha) polypeptides were overproduced, whereas significant levels of early (beta) and drastically reduced levels of several late (gamma) proteins were synthesized at the nonpermissive temperature. Interestingly, the mutants were observed to form a spectrum with regard to their relative abilities to induce the expression of a number of polypeptides, especially those of the delayed-early (beta gamma) class. Consistent with their ability to induce expression of early polypeptides, all of the mutants induced the synthesis of substantial levels of viral DNA at the nonpermissive temperature. Taken together, the results of these studies demonstrate that ICP27 plays an essential regulatory function in virus replication, that this function is required after the onset of early gene expression and viral DNA synthesis, and that the inability of the mutants to induce the synthesis of late proteins is independent of viral DNA synthesis.

Mutations in the herpes simplex virus major DNA-binding protein gene leading to altered sensitivity to DNA polymerase inhibitors

Five herpes simplex virus mutants containing temperature-sensitive mutations in the gene for the major DNA-binding protein were assayed for their sensitivities to the DNA polymerase inhibitors aphidicolin and phosphonoacetic acid (PAA). Four of the mutants (tsA1, tsA15, tsA24, and tsA42) exhibited altered sensitivity to one or both of the inhibitors relative to the wild-type parent. In tsA1, a mutation or mutations conferring aphidicolin and PAA hypersensitivity were mapped by corescue with the temperature-sensitivity marker of tsA1 to a region of the DNA-binding protein locus, between map coordinates 0.385 and 0.398. The mutation conferring PAA hypersensitivity in tsA24 similarly corescued with the tsA24 temperature-sensitivity marker, mapping to the DNA-binding protein locus between coordinates 0.398 and 0.413. Thus, mutations outside the DNA polymerase locus and within the DNA-binding protein locus can confer altered sensitivity to certain DNA polymerase inhibitors. Assays of the aphidicolin and PAA sensitivities of ts+ recombinants derived by marker rescue of the DNA-binding protein mutants revealed the presence of additional mutations, separable from the ts mutations, in each of three mutants examined. One such mutation, which contributed to the aphidicolin-hypersensitivity phenotype of tsA1, mapped between coordinates 0.422 and 0.448, and resides, most probably, within the DNA polymerase locus. These additional mutations possibly confer compensating modifications to the DNA polymerase such that functional interaction with altered DNA-binding protein is restored. These findings provide strong evidence that the major DNA-binding protein and the DNA polymerase of herpes simplex virus interact in infected cells.

Cloning, sequencing, and functional analysis of oriL, a herpes simplex virus type 1 origin of DNA synthesis

The herpes simplex virus type 1 genome (160 kilobases) contains three origins of DNA synthesis: two copies of oriS located within the repeated sequences flanking the short unique arm (US), and one copy of oriL located within the long unique arm (UL). Precise localization and characterization of oriL have been severely hampered by the inability to clone sequences which contain it (coordinates 0.398 to 0.413) in an undeleted form in bacteria. We report herein the successful cloning of sequences between 0.398 to 0.413 in an undeleted form, using a yeast cloning vector. Sequence analysis of a 425-base pair fragment spanning the deletion-prone region has revealed a perfect 144-base pair palindrome with striking homology to oriS. In a functional assay, the undeleted clone was amplified when functions from herpes simplex virus type 1 were supplied in trans, whereas clones with deletions of 55 base pairs or more were not amplified.

Cloning, sequencing, and functional analysis of oriL, a herpes simplex virus type 1 origin of DNA synthesis

The herpes simplex virus type 1 genome (160 kilobases) contains three origins of DNA synthesis: two copies of oriS located within the repeated sequences flanking the short unique arm (US), and one copy of oriL located within the long unique arm (UL). Precise localization and characterization of oriL have been severely hampered by the inability to clone sequences which contain it (coordinates 0.398 to 0.413) in an undeleted form in bacteria. We report herein the successful cloning of sequences between 0.398 to 0.413 in an undeleted form, using a yeast cloning vector. Sequence analysis of a 425-base pair fragment spanning the deletion-prone region has revealed a perfect 144-base pair palindrome with striking homology to oriS. In a functional assay, the undeleted clone was amplified when functions from herpes simplex virus type 1 were supplied in trans, whereas clones with deletions of 55 base pairs or more were not amplified.

Temperature-sensitive mutants in herpes simplex virus type 1 ICP4 permissive for early gene expression

A large number of temperature-sensitive (ts) mutants of herpes simplex virus type 1 (HSV-1) in the gene encoding the immediate-early transcriptional regulatory protein, ICP4, have been isolated and characterized with respect to expression of the immediate-early, early, and late viral gene products. The hallmark of these mutants is the overproduction of immediate-early gene products and the underproduction of early and late gene products. The present study involves the preliminary genetic and molecular characterization of two unique regulatory mutants of HSV-1, ts48 and ts303. Genetically, both mutants exhibit inefficient complementation with eight ts mutants in complementation group 1-2, which defines the gene for ICP4, and marker rescue experiments place the mutations in both mutants in the 3' portion of the coding sequence for ICP4. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of ts48- and ts303-infected cell polypeptides synthesized at the nonpermissive temperature demonstrates that immediate-early polypeptides ICP4 and ICP27 are overproduced, with the simultaneous production of early polypeptides ICP6, ICP8, gB, and others. Immediate-early polypeptides are resynthesized upon temperature shift-up early in infection; however, shift-up late in infection does not result in the resynthesis of immediate-early polypeptides. Late gene products are either absent or underrepresented under long-term labeling conditions. To examine the effects of the mutations in ts48, ts303, and other ICP4 mutants specifically on early gene expression, trans-induction experiments were performed in cells transfected with the gene for chloramphenicol acetyltransferase under early gene control (tk) and superinfected with KOS, tsB32, ts48, and ts303. Mutant tsB32 did not induce chloramphenicol acetyltransferase activity above the basal level; however, ts48 and ts303 induced chloramphenicol acetyltransferase activity nearly equal to wild-type levels. Fifteen to fifty percent of wild-type levels of viral DNA are synthesized at the nonpermissive temperature in ts48- and ts303-infected cells, indicating that immediate-early and early gene functions are intact (or nearly so) and that the block in ts48 and ts303 is in a regulatory event subsequent to that exhibited by other mutants in complementation group 1-2 which are DNA-.

Characterization of an aphidicolin-resistant mutant of herpes simplex virus type 2 which induces an altered viral DNA polymerase

The replication of wild-type herpes simplex virus type 2 (HSV-2) was very sensitive to aphidicolin, a specific inhibitor of eukaryotic alpha-type DNA polymerases; viral DNA synthesis was strongly inhibited by 1 microgram/ml of aphidicolin, but the synthesis of early viral polypeptides was not affected. Using aphidicolin as the selective agent, aphidicolin-resistant ( Aphr ) viruses were isolated from HSV-2 strain 186. All of these plaque isolates induced altered viral DNA polymerases which were more resistant to aphidicolin than wild-type polymerase. These results clearly indicate that viral DNA polymerase is a target of aphidicolin in vivo and suggest that host cell DNA polymerase alpha may be not involved in the replication of HSV-2. Partially purified mutant polymerase exhibited a 7.5-fold lower apparent Km for dCTP and a 3-fold lower apparent Km for dTTP than similarly purified wild-type enzyme. The apparent Ki value for aphidicolin of the mutant polymerase was 6.5-fold higher than that of the wild-type enzyme. Moreover, all Aphr viruses isolated were also resistant to thymine-1-beta-D-arabinofuranoside (ara-T). While, they were as sensitive as wild-type virus to cytosine-1-beta-D-arabinofuranoside (ara-C), adenine-9-beta-D-arabinofuranoside (ara-A), and acycloguanosine (acyclo-G). Interestingly these Aphr isolates were more sensitive to phosphonoacetic acid (PAA) than the wild-type. In contrast, PAA-resistant ( PAAr ) viruses of HSV-2 were more sensitive to aphidicolin and were more resistant to all of four nucleoside analogs than the parental wild-type virus. These results suggest that the aphidicolin-binding site of HSV DNA polymerase may be very close to the binding sites for dCTP and dTTP and it functionally correlates with that for pyrophosphate group.

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

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

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

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

Detection of herpes simplex virus intertypic recombinant genomes in infected cell DNA

Intertypic recombination between herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) was detected using DNA from mixedly infected cells. Because HSV-1 and HSV-2 share a 50% base sequence homology along the genome but have markedly different DNA restriction enzyme cleavage patterns, recombination events can be detected and quantified by analysis of restriction endonuclease digests for the presence of novel DNA fragments. We have used this technique to quantify the degree of interference by HSV-2 on HSV-1 replication as well as the effect of limiting the availability of one genome on the frequency of intertypic recombination. Because this technique does not require production of viable progeny virions, it should also be useful for studying early recombination events.

Fine mapping and molecular cloning of mutations in the herpes simplex virus DNA polymerase locus

Mutations in five phenotypically distinct mutants derived from herpes simplex virus type 1 strain KOS which lie in or near the herpes simplex virus DNA polymerase (pol) locus have been fine mapped with the aid of cloned fragments of mutant and wild-type viral DNAs to distinct restriction fragments of 1.1 kilobase pairs (kbp) or less. DNA sequences containing a mutation or mutations conferring resistance to the antiviral drugs phosphonoacetic acid, acyclovir, and arabinosyladenine of pol mutant PAAr5 have been cloned as a 27-kbp Bg+II fragment in Escherichia coli. These drug resistance markers have been mapped more finely in marker transfer experiments to a 1.1-kbp fragment (coordinates 0.427 to 0.434). In intratypic marker rescue experiments, temperature-sensitive (ts), phosphonoacetic acid resistance, and acyclovir resistance markers of pol mutant tsD9 were mapped to a 0.8-kbp fragment at the left end of the EcoRI M fragment (coordinates 0.422 to 0.427). The ts mutation of pol mutant tsC4 maps within a 0.3-kbp sequence (coordinates 0.420 to 0.422), whereas that of tsC7 lies within the 1.1-kbp fragment immediately to the left (coordinates 0.413 to 0.420). tsC4 displays the novel phenotype of hypersensitivity to phosphonoacetic acid; however, the phosphonoacetic acid hypersensitivity phenotype is almost certainly not due to the mutation(s) conferring temperature sensitivity. The ts mutation of mutant tsN20--which does not affect DNA polymerase activity--maps to a 0.5-kbp fragment at the right-hand end of the EcoRI M fragment (coordinates 0.445 to 0.448). The mapping of the mutations in these five mutants further defines the limits of the pol locus and separates mutations differentially affecting catalytic functions of the polymerase.

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

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

Genetic 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.

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

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

Localization of the regions of homology between the genomes of herpes simplex virus, type 1, and pseudorabies virus

Only 8% of the sequences of the genomes of pseudorabies (PRV) and herpes simplex (type 1) (HSV) viruses are homologous. These homologous sequences have been shown previously to be distributed throughout most of the genomes of the two viruses. By means of blot hybridization of restriction fragments of HSV-1 DNA to cloned, nick-translated restriction fragments of PRV DNA, it was possible to compare the location on the genomes of these viruses of the homologous regions. The results showed that the genome of PRV is, for the most part, colinear with the IL arrangement of the genome of HSV-1. An inversion or translocation of sequences mapping on the PRV genome between 0.07 and 0.39 map units was observed on the genome of one of these viruses. A comparison of the map positions of five genes with known functions confirmed these findings. The genes coding for the major immediate-early protein, the major capsid protein, and the thymidine kinase occupy similar positions on the genome of PRV and on the genome of HSV-1 in the IL arrangement. However, the genes for DNA polymerase and for the major DNA binding protein appear to be inverted relative to one another on the genomes of the two viruses.

Genetic analysis of temperature-sensitive mutants which define the gene for the major herpes simplex virus type 1 DNA-binding protein

We have assigned eight temperature-sensitive mutants of herpes simplex virus type 1 to complementation group 1-1. Members of this group fail to complement mutants in herpes simplex virus type 2 complementation group 2-2. The mutation of one member of group 1-1, tsHA1 of strain mP, has been shown to map in or near the sequence which encodes the major herpes simplex virus type 1 DNA-binding protein (Conley et al., J. Virol. 37:191-206, 1981). The mutations of five other members of group 1-1 map in or near the sequence in which the tsHA1 mutation maps, a sequence which lies near the center of UL between the genes for the viral DNA polymerase and viral glycoprotein gAgB. These mutants can be divided into two groups; the mutations of one group map between coordinates 0.385 and 0.398, and the mutations of the other group map between coordinates 0.398 and 0.413. At the nonpermissive temperature mutants in group 1-1 are viral DNA negative, and mutant-infected cells fail to react with monoclonal antibody to the 130,000-dalton DNA-binding protein. Taken together, these data indicate that mutants in complementation groups 1-1 and 2-2 define the gene for the major herpes simplex virus DNA-binding protein, an early gene product required for viral DNA synthesis.

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.