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

Herpes simplex virus ICP27 increases translation of a subset of viral late mRNAs

The herpes simplex virus (HSV) ICP27 immediate-early protein plays an essential role in the expression of viral late genes. ICP27 is a multifunctional protein and has been reported to regulate multiple steps of mRNA synthesis and processing, including transcription, splicing, and nuclear export. Recently, ICP27 was reported to interact with translation factors and to stimulate translation of the viral late mRNA encoding VP16. We examined the effects of ICP27 on accumulation, nuclear export, and translation of HSV 1 (HSV-1) late mRNAs encoding VP16, ICP5, and gD. We confirm here that ICP27 stimulates translation of VP16 mRNA as well as an additional HSV-1 late ICP5 mRNA. The data presented here demonstrate that translation levels of both VP16 and ICP5 mRNA is reduced during infections with the ICP27-null virus mutant d27-1, and with ICP27 C-terminal deletion mutant viruses n406 and n504, compared to wild-type virus. In contrast, the translation of gD mRNA is not affected by the presence of ICP27 during infection. These data demonstrate that ICP27 functions to increase the translation levels of a subset of HSV-1 late genes, and this function requires the C terminus of ICP27.

Multiarm high-throughput integration site detection: limitations of LAM-PCR technology and optimization for clonal analysis

Retroviral integration provides a unique and heritable genomic tag for a target cell and its progeny, enabling studies of clonal composition and repopulation kinetics after gene transfer into hematopoietic stem cells. The clonal tracking method, linear amplification-mediated polymerase chain reaction (LAM-PCR) is widely employed to follow the hematopoietic output of retrovirally marked stem cells. Here we examine the capabilities and limitations of conventional LAM-PCR to track individual clones in a complex multiclonal mix. Using artificial mixtures of retrovirally marked, single-cell-derived clones, we demonstrate that LAM-PCR fails to detect 30-40% of the clones, even after exhaustive analysis. Furthermore, the relative abundance of specific clones within a mix is not accurately represented, deviating by as much as 60-fold from their true abundance. We describe an optimized, multiarm, high-throughput modification of LAM-PCR that improves the global detection capacity to greater than 90% with exhaustive sampling, facilitates accurate estimates of the total pool size from smaller samplings, and provides a rapid, cost-effective approach to the generation of large insertion-site data bases required for evaluation of vector integration preferences. The inability to estimate the abundance of individual clones within mixtures remains a serious limitation. Thus, although LAM-PCR is a powerful tool for identification of integration sites and for estimations of clonal complexity, it fails to provide the semiquantitative information necessary for direct, reliable tracking of individual clones in a chimeric background.

Morphologic, immunohistochemical, immunologic, ultrastructural, and time-related study of herpes simplex virus type 1-infected cultured human fibroblasts

Membrane glycoproteins of enveloped animal viruses are synthesized, processed, and transported inside infected cells. Expression of viral glycoproteins on the surface of viral particles and host cells are essential for many biologic functions. In the case of herpes simplex virus, the glycoprotein molecules may act as nucleation points for virus assembly and budding at the nuclear membrane. The temporal distribution of herpes simplex virus type 1 particles and glycoproteins in cultured human fibroblasts was studied by titration plaque assay, immunoblots, immunofluorescence light microscopy, and immunogold cryosection electron microscopy to describe the virus-cell interactions. These concordant analyses revealed significant release of infectious viral particles to the medium at 6 hours postinfection, that the capacity of the host cells to make infectious viral particles was complete at 18 hours postinfection, and that the infection brought time-related modifications of tubulin, cell morphology, and viral glycoproteins. The data presented is in accord with the theory of envelopment at the nuclear membranes containing immature glycoproteins followed by multiple deenvelopments and reenvelopments of the virus particles during the transport and maturation in the endoplasmic reticulum and the Golgi complex.

Herpes simplex type 1:lacZ recombinant viruses. I. Characterization and application to defining the mechanisms of action of known antiherpes agents

Recombinant viruses with the lacZ gene placed under the control of the HSV-1 ICP4, TK and gD regulatory regions were constructed by recombination into the TK locus of HSV-1. Difficulty in isolating ICP4 and gD recombinant viruses with high level, regulated expression of beta-galactosidase was overcome by the use of HSV-1 translational initiation sequences of these genes in place of vector-derived sequences. beta-Galactosidase expression displayed the kinetics particular to each viral class. The maximal expression of beta-galactosidase from the recombinant viruses within a 22-h period (m.o.i. 5) (relative to the ICP4 virus) was gD(3) > gC(2) > ICP4(1) > TK(0.5). The ICP4 virus produces easily quantifiable levels of beta-galactosidase activity for multiplicities of infection from 5 x 10(-4) through 5 over 48 h postinfection. At multiplicities of infection between 2 and 5, ICP4-driven activity was measurable within 2 h postinfection from a monolayer of 3 x 10(4) Vero cells in microtiter wells. Mechanisms of inhibition of several antivirals were probed by using the regulated expression of beta-galactosidase from the ICP4 virus as a marker for viral growth. An experimental antiviral (E3925, IC50 1 microgram/ml) and a neutralizing gD MAb (DUP55306, IC50 0.6 microgram/ml) acted prior to immediate early synthesis, consistent with inhibition of viral entry or uncoating. IFN-gamma inhibited expression of immediate-early synthesis, while having no effect on viral entry. IC50 values for E3925 obtained using either the ICP4 or gD viruses at m.o.i. 0.005, were in good agreement with those obtained by standard plaque assays, but were determined in only 1 day, using a microtiter plate format. Thus, these reporter viruses are useful tools for defining the mechanisms of action of antiherpes agents, while quantitatively reproducing the results for IC50 determinations from standard plaque assays within 24 h in a microtiter plate format.

Herpes simplex type1:lacZ recombinant viruses. II. Microtiter plate-based colorimetric assays for the discovery of new antiherpes agents and the points at which such agents disrupt the viral replication cycle

A panel of microtiter plate-based colorimetric assays for monitoring HSV-1 growth has been made. The panel consists of 4 different HSV-1 (strain KOS) lacZ recombinant viruses which express beta-galactosidase under the control of different HSV-1 promoters derived from each class of herpes simplex gene expression: immediate-early (ICP4), early (TK), delayed early (gD) and late (gC). Inhibitors of HSV-1 growth were evaluated using differential effects on each of the reporter viruses as a measure of which points in the viral replication cycle an inhibitor was acting. Aphidicolin (DNA synthesis inhibitor) was studied as a model compound. At an m.o.i. of 0.05, at 24 h postinfection (h p.i.), aphidicolin inhibited 80% of viral growth at 1 micrograms/ml, as determined by a reduction in ICP4-driven activity within the second cycle of infection. At m.o.i. 5, within the first infectious cycle, aphidicolin had no effect on the signals from either the ICP4 or TK viruses at 3 micrograms/ml, while largely suppressing gD and fully inhibiting gC-driven signals at 2 micrograms/ml. This profile is consistent with the behavior expected of a DNA synthesis inhibitor. Five inhibitors of unknown mechanism were evaluated. Two compounds inhibited ICP4-driven activity within the first infectious cycle and were classified as potential inhibitors of viral entry, uncoating or IE gene expression (XF884, BT318). One compound inhibited gD and gC-driven activity without inhibiting signal from the ICP4 and TK viruses, and was classified as a potential DNA synthesis inhibitor (DS810). Two compounds (S5193, ER622) had effects on gD- and gC-driven activity which were somewhat different from aphidicolin and DS810, but which could be interpreted as inhibition of viral assembly and/or egress. The potency of XF884 varied with the time postinfection at which it was added to cells (IC50 3.7 to > 10 micrograms/ml) while the effects of BT318 were independent of time of addition (IC50 11.4 micrograms/ml). These results suggest XF884 inhibits viral entry while BT318 is acting after viral entry, possibly as a direct inhibitor of ICP4 gene expression. Together, these results suggest the panel of recombinant herpes viruses has utility in aiding in the identification of the points in the herpes life cycle at which antiherpes drug candidates, of unknown mechanisms, are acting.

Equine herpesvirus 1 glycoprotein D: mapping of the transcript and a neutralization epitope

Studies with molecular and immunological techniques identified and mapped the transcript encoding glycoprotein D (gD) of equine herpesvirus 1 KyA, as well as two continuous gD antigenic determinants. Three mRNA species of 5.5, 3.8, and 1.7 kb overlap the gD open reading frame and are transcribed from the DNA strand encoding gD. Northern (RNA) blot hybridization with both DNA clones and riboprobes, as well as S1 nuclease analyses, showed the 3.8-kb mRNA to encode gD and to be synthesized as a late (beta-gamma) transcript. The 3.8-kb gD mRNA initiates within the US segment 91 and 34 nucleotides downstream of the CCAAT and TATA elements, respectively, and encodes a potential polypeptide of 392 amino acids. The termination site of this transcript maps within the terminal repeat at a site also used by the 5.5-kb mRNA and the IR6-encoded 1.2-kb mRNA, such that these three transcripts form a 3'-coterminal nested set. The extended size (2,250 nucleotides) of the 3' untranslated region of the gD transcript and its termination within the terminal repeat may result from the deletion of 3,859 bp, which eliminates two consensus polyadenylation signals downstream of the gD open reading frame of EHV-1 KyA. Use of antisera to synthetic peptides of 19 amino acids (residues 4 to 22) and 20 amino acids (residues 267 to 285) in Western immunoblot analyses revealed that gD is present in EHV-1 virions as a 55-kDa polypeptide. In addition, these antisera detected the 55-kDa protein as well as 58- and 47-kDa polypeptides in infected-cell extracts at late times of infection. Residues 4 to 22 make up a continuous neutralizing epitope of gD, since incubation of equine herpesvirus 1 with the anti-19-mer serum prior to infection results in reduced numbers of plaques and reduced levels of virus-encoded thymidine kinase. Complement is not required for neutralization mediated by the anti-19-mer serum.

Kinetics of expression of the gene encoding the 65-kilodalton DNA-binding protein of herpes simplex virus type 1

The 65-kilodalton DNA-binding protein (65KDBP) of herpes simplex virus type 1, encoded by gene UL42, is required for herpes simplex virus origin-dependent DNA replication (C.A. Wu, N.J. Nelson, D.J. McGeoch, and M.D. Challberg, J. Virol. 62:435-443, 1988). We found by indirect immunofluorescence with monoclonal antibody to 65KDBP that the protein was first detectable at 3 h postinfection. It localized first to the inner periphery of the nucleus, but accumulated in large globular compartments within the nucleus by 6 h postinfection in a pattern similar to that displayed by the major DNA-binding protein ICP8. Immune electron microscopy revealed that 65KDBP was associated with the marginated heterochromatin at the early times, but migrated further into the nucleus at late times when the only discernible areas devoid of 65KDBP were the nucleoli and heterochromatin. The 65KDBP gene is a member of the beta kinetic class as determined by the ability of the mRNA to be expressed at significant levels even in the absence of viral DNA synthesis. Furthermore, in the presence or absence of the DNA polymerase inhibitor phosphonoacetic acid, the patterns of accumulation of protein as well as mRNA were virtually indistinguishable from those displayed by the model beta genes encoding ICP8 and thymidine kinase. Nuclear run-on experiments demonstrated that maximum rates of 65KDBP gene transcription occurred prior to the maximum rate of progeny viral DNA synthesis and confirmed that the expression of the 65KDBP gene is regulated at the level of transcriptional initiation.

Analysis of the transcript of the herpes simplex virus DNA polymerase gene provides evidence that polymerase expression is inefficient at the level of translation

We have mapped the termini and determined the relative abundance and ribosome density of the major cytoplasmic transcript of the DNA polymerase (pol) gene of herpes simplex virus type 1. Nuclease protection and primer extension analyses located the 5' end of the major pol transcript at two closely spaced sites 51 and 57 nucleotides to the left of a BamHI site at map position 0.413. S1-sensitive sites corresponding to additional minor transcripts were found to map further upstream within a palindromic sequence that contains a viral replication origin. The major 3' end was found to map 90 nucleotides upstream of a KpnI site at map position 0.439. Quantitative S1 nuclease assays revealed that pol transcripts were nearly as abundant as transcripts encoded by the viral thymidine kinase gene. However, relatively few pol transcripts were found on large polysomes at 5.5 h after infection, when pol transcripts were most abundant. This was in marked contrast to the polyribosome distribution of transcripts from the thymidine kinase gene and the major DNA-binding protein gene. These results and sequence features of the pol transcript suggest that pol expression is regulated, in part, at the level of translation.

Evidence that transcriptional control is the major mechanism of regulation for the glycoprotein D gene in herpes simplex virus type 1-infected cells

In this report, we demonstrate a close correlation between the levels of steady-state mRNA, polysome-associated RNA, and the rate of protein synthesis for glycoprotein D, a beta-gamma product of herpes simplex virus type 1, and for the model beta (ICP8), beta-gamma (glycoprotein B), and gamma (glycoprotein C) gene products included in this study as controls. No evidence was found for posttranscriptional control of expression of these products. We conclude from these results that the major regulatory control for these genes during herpes simplex virus type 1 infection is transcriptional.

Regulation of glycoprotein D synthesis: does alpha 4, the major regulatory protein of herpes simplex virus 1, regulate late genes both positively and negatively?

Earlier studies have described the alpha 4/c113 baby hamster kidney cell line which constitutively expresses the alpha 4 protein, the major regulatory protein of herpes simplex virus 1 (HSV-1). Introduction of the HSV-1 glycoprotein B (gB) gene, regulated as a gamma 1 gene, into these cells yielded a cell line which constitutively expressed both the alpha 4 and gamma 1 gB genes. The expression of the gB gene was dependent on the presence of functional alpha 4 protein. In this article we report that we introduced into the alpha 4/c113 and into the parental BHK cells, the HSV-1 BamHI J fragment, which encodes the domains of four genes, including those of glycoproteins D, G, and I (gD, gG, and gI), and most of the coding sequences of the glycoprotein E (gE) gene. In contrast to the earlier studies, we obtained significant constitutive expression of gD (also a gamma 1 gene) in a cell line (BJ) derived from parental BHK cells, but not in a cell line (alpha 4/BJ) which expresses functional alpha 4 protein. RNA homologous to the gD gene was present in significant amounts in the BJ cell line; smaller amounts of this RNA were detected in the alpha 4/BJ cell line. RNA homologous to gE, presumed to be polyadenylated from signals in the vector sequences, was present in the BJ cells but not in the alpha 4/BJ cells. The expression of the HSV-1 gD and gE genes was readily induced in the alpha 4/BJ cells by superinfection with HSV-2. The BJ cell line was, in contrast, resistant to expression of HSV-1 and HSV-2 genes. The BamHI J DNA fragment copy number was approximately 1 per BJ cell genome equivalent and 30 to 50 per alpha 4/BJ cell genome equivalent. We conclude that (i) the genes specifying gD and gB belong to different viral regulatory gene subsets, (ii) the gD gene is subject to both positive and negative regulation, (iii) both gD and gE mRNAs are subject to translational controls although they may be different, and (iv) the absence of expression of gD in the alpha 4/BJ cells reflects the expression of the alpha 4 protein in these cells.

Dissection of immediate-early gene promoters from herpes simplex virus: sequences that respond to the virus transcriptional activators

The immediate-early promoters of herpes simplex virus give rise to the first series of transcripts after infection. These promoters are composed of compound sequence elements that govern basal level and regulated transcription. The response of three core (truncated) promoters from the herpes simplex virus type 1 IE-4, IE-0, and IE-27 genes to a battery of virus-encoded trans-acting proteins was examined in a short-term transient expression assay system. The results of this study reveal (i) a role for a sequence, 5'---GGGGG---3', flanked by 3 to 5 base pairs of symmetry (the G box), which is present in the upstream region of all immediate-early gene promoters, (ii) a requirement for the consensus sequence protected by ICP4 for autoregulation by this immediate-early gene product, and (iii) an alternative, sequence-independent mechanism for the augmentation of alpha gene expression by the virion-associated transcriptional activator Vmw65, now designated as TIF.

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.

Herpes simplex virus virion stimulatory protein mRNA leader contains sequence elements which increase both virus-induced transcription and mRNA stability

To investigate the role of 5' noncoding leader sequence of herpes simplex virus type 1 (HSV-1) mRNA in infected cells, the promoter for the 65,000-dalton virion stimulatory protein (VSP), a beta-gamma polypeptide, was introduced into plasmids bearing the chloramphenicol acetyltransferase (cat) gene together with various lengths of adjacent viral leader sequences. Plasmids containing longer lengths of leader sequence gave rise to significantly higher levels of CAT enzyme in transfected cells superinfected with HSV-1. RNase T2 protection assays of CAT mRNA showed that transcription was initiated from an authentic viral cap site in all VSP-CAT constructs and that CAT mRNA levels corresponded to CAT enzyme levels. Use of cis-linked simian virus 40 enhancer sequences demonstrated that the effect was virus specific. Constructs containing 12 and 48 base pairs of the VSP mRNA leader gave HSV infection-induced CAT activities intermediate between those of the leaderless construct and the VSP-(+77)-CAT construct. Actinomycin D chase experiments demonstrated that the longest leader sequences increased hybrid CAT mRNA stability at least twofold in infected cells. Cotransfection experiments with a cosmid bearing four virus-specified transcription factors (ICP4, ICP0, ICP27, and VSP-65K) showed that sequences from -3 to +77, with respect to the viral mRNA cap site, also contained signals responsive to transcriptional activation.

Kinetics of expression of herpes simplex virus type 1-specific glycoprotein species on the surfaces of infected murine, simian, and human cells: flow cytometric analysis

The kinetics of expression of the herpes simplex virus type 1-encoded major glycoprotein species gB, gC, gD, and gE on the surfaces of cells of murine, simian, and human origins were studied. Viable cells were stained with monoclonal antibodies specific for each species, and the levels expressed were determined by fluorescence flow cytometry. Differences were observed in both the kinetics and the levels of expression of individual glycoprotein species, depending upon the origin of the host cells. Glycoprotein gC was expressed early and at high levels in cells of murine and human origins, but late and at relatively low levels in simian cells. In contrast, gE was expressed at high levels in simian cells, but was not detectable until late in the infectious cycle in murine and human cells. The kinetics and levels of expression of gB were similar for all cells investigated, whereas gD, with high levels of expression in all cells late in infection, appeared on the surfaces of murine cells very early postinfection. This approach has allowed a simple quantitative method for comparing levels of glycoprotein expression.

A single regulatory region modulates both cis activation and trans activation of the herpes simplex virus VP5 promoter in transient-expression assays in vivo

A detailed analysis of the expression of the bacterial chloramphenicol acetyltransferase gene controlled by the herpes simplex virus major capsid protein (VP5) promoter showed that this promoter can be functionally separated into an 80-base core region, which has the minimal information required to serve as a pol II promoter but which is not fully activated by viral superinfection or by cotransfections with plasmids bearing functional alpha (immediate-early) genes, and an approximately 100-base regulatory region upstream of the core, which allowed full induction of VP5 promoter-driven chloramphenicol acetyltransferase activity but which repressed the ability of the VP5 core promoter to be cis activated by the simian virus 40 enhancer. This was in distinct contrast to the situation with the alkaline exonuclease promoter (a model early promoter) and defined the regions of this promoter which can be used to study the interaction between viral promoters and putative regulatory proteins induced by viral infection.

Co-ordinate regulation of herpes simplex virus gene expression is mediated by the functional interaction of two immediate early gene products

At early times after infection with herpes simplex virus, transcription from beta-promoters is initiated only in the presence of a functional 174,000 Mr phosphoprotein (ICP4), encoded by an immediate early (alpha) gene (IE4). A transient expression assay was used to analyze the requirement for two (ICP4 and ICP0) of the five alpha-gene products in the transcriptional regulation of model alpha and beta-gene promoters. These studies reveal that cells cotransfected with plasmids containing the alpha-gene sequences for infected cell proteins (ICPs) 4 and 0 and a thymidine kinase (TK, a beta-gene) gene or the thymidine kinase promoter fused to a chloramphenicol acetyltransferase (CAT) cassette accumulate 10 to 20-fold more RNA or exhibit 10 to 20-fold more CAT activity than cells cotransfected with a plasmid encoding either alpha-gene protein and a thymidine kinase indicator gene. Functional ICP4 is required for enhanced transcriptional activation in the transient expression assay system. It is also required for the uniform dispersal of ICP0 throughout the nucleus as shown by immunofluorescence staining analysis of transfected cells. Two alpha-promoter-CAT fusions were used as targets to study what effects ICP4, ICP0 and Vmw65 (the virion-associated alpha-gene transactivator) have on expression from alpha-promoters that contain all of the sequences that confer alpha-gene regulation, or only the core sequence governing basal level expression. We conclude that ICP4 can activate alpha-gene expression from the core sequence and, depending on its abundance, activate or repress expression from a promoter containing the sequences required for alpha-gene regulation. Independent of these alpha-regulatory sequences cotransfection with low levels of sequences encoding both ICP0 and ICP4 activate expression. At higher ratios of effector (both ICP4 and ICP0) the target accumulation of CAT activity decreases. Although a ts allele of IE4 (cloned from the mutant virus tsK) does not activate alpha-gene expression it can enhance the ability of ICP0 to activate a target containing alpha-regulatory sequences. Virus studies involving tsK support the conclusion that functional ICP4 is required to activate beta-promoters and to repress expression from alpha-promoters and help to explain the pleiotropic effects of the tsK mutation. These analyses have also revealed the presence of a novel RNA species that overlaps the sequences encoding ICP0. Our results suggest that co-ordinate regulation of HSV gene expression is mediated by the functional interaction of at least two alpha-gene products, ICP0 and ICP4.

A cis-acting element within the 5' leader of a cytomegalovirus beta transcript determines kinetic class

During cytomegalovirus (CMV) infection, gene expression is regulated by transcriptional and posttranscriptional events. Although recent studies have established that posttranscriptional controls are important determinants of gene expression in several eukaryotic systems, the precise signals and mechanisms have not been clearly identified. We present evidence for a cis-acting signal, contained within the 5' leader region of a CMV beta (or early) gene, that acts posttranscriptionally in the regulation of gene expression. Addition of this signal to an alpha (or immediate early) gene construct converted expression of the indicator protein to the beta class, even though the gene remained under alpha transcriptional control. Deletion of a portion of the beta gene leader sequence (nucleotides +62 to +142) reverted expression to the alpha class. This cis-dominant signal appears to act by blocking expression posttranscriptionally until a viral function activates full gene expression at the appropriate time in infection.

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.

DNA replication is required for abundant expression of a plasmid-borne late US11 gene of herpes simplex virus type 1

During herpes simplex virus type 1 (HSV-1) infection, the appearance of true-late gene products is severely reduced under conditions of DNA synthesis inhibition. This report describes the use of a plasmid-borne promoter of a true-late HSV-1 gene (US11), linked to the rabbit beta-globin gene, to study the requirement of DNA replication for late gene expression. The activity of the plasmid-borne US11 promoter in constructs containing or lacking an HSV-1 origin of replication (ORIS) was analysed by quantitative S1 mapping of correctly initiated hybrid transcripts. Following HSV-1 superinfection of transfected HeLa cells, the US11 promoter in ORI+ plasmids was expressed with similar kinetics to the viral US11 promoter. US11 promoter activity was first detected at the same time as the onset of DNA template replication. Expression of US11 RNA was detectable from non-replicating ORI- plasmids, although transcript accumulation was reduced by greater than 90%. Sequences containing the IE-5 promoter (a 3' co-terminal gene whose transcription starts 5' of US11) also played a positive role in achieving normal US11 gene expression.

Regulation of protein synthesis in virus-infected animal cells

This chapter summarizes the structural features that govern the translation of viral mRNAs: where the synthesis of a protein starts and ends, how many proteins can be produced from one mRNA, and how efficiently. It focuses on the interplay between viral and cellular mRNAs and the translational machinery. That interplay, together with the intrinsic structure of viral mRNAs, determines the patterns of translation in infected cells. It also points out some possibilities for translational regulation that can only be glimpsed at present, but are likely to come into focus in the future. The mechanism of selecting the initiation site for protein synthesis appears to follow a single formula. The translational machinery displays a certain flexibility that is exploited more frequently by viral than by cellular mRNAs. Although some of the parameters that determine efficiency have been identified, how efficiently a given mRNA will be translated cannot be predicted by summing the known parameters.

Virus-induced modification of the host cell is required for expression of the bacterial chloramphenicol acetyltransferase gene controlled by a late herpes simplex virus promoter (VP5)

The requirements for expression of genes under the control of early (alkaline exonuclease) and late (VP5) herpes simplex virus type 1 (HSV-1) gene promoters were examined in a transient expression assay, using the bacterial chloramphenicol acetyltransferase gene as an expression marker. Both promoters were induced, resulting in the production of high levels of the enzyme upon low-multiplicity infection by HSV-1. S1 nuclease analysis of hybrids between RNA isolated from infected cells containing HSV-1 promoter constructs and marker gene DNA demonstrated normal transcriptional initiation of the marker gene directed by the viral promoters. Viral DNA sequences no more than 125 bases 5' of the putative transcriptional cap site were sufficient for maximum activity of the late promoter. In contrast to expression controlled by the early gene, the late promoter was not active at a measurable level in uninfected cells until DNA sequences between 75 and 125 bases 5' of the transcriptional cap site were deleted. Cotransfection of cells with the expression marker controlled by HSV promoters and a cosmid containing HSV alpha (immediate-early) genes indicated that full expression of both early and late promoters requires the same virus-induced host cell modifications. Inhibition of viral DNA synthesis results in an increased rate of transient expression of marker genes under control of either early or late promoters in contrast to the situation in normal virus infection. These data provide evidence that the normal course of expression of late HSV genes involves negative modulation of potentially active promoters in the infected cell.

Intracellular transport of herpes simplex virus gD occurs more rapidly in uninfected cells than in infected cells

A mouse L cell line which expresses the herpex simplex virus type 1 immediate-early polypeptides ICP4 and ICP47 was cotransfected with a cloned copy of the BglII L fragment of herpes simplex virus type 2, which includes the gene for gD, and the plasmid pSV2neo, which contains the aminoglycosyl 3'-phosphotransferase (agpt) gene conferring resistance to the antibiotic G418. A G418-resistant transformed cell line was isolated which expressed herpes simplex virus type 2 gD at higher levels than were found in infected cells. The intracellular transport and processing of gD was compared in transformed and infected cells. In the transformed Z4/6 cells gD was rapidly processed and transported to the cell surface; in contrast, the processing and cell surface appearance of gD in infected parental Z4 cells occurred at a much slower rate, and gD accumulated in nuclear membrane to a greater extent. Thus, the movement of HSV-2 gD to the cell surface in infected cells is retarded as viral glycoproteins accumulate in the nuclear envelope, probably because they interact with other viral structural components.

Evidence for a direct role for both the 175,000- and 110,000-molecular-weight immediate-early proteins of herpes simplex virus in the transactivation of delayed-early promoters

We reconstructed the regulated induction of delayed-early (DE) transcription that occurs during herpes simplex virus (HSV) infection by using a transient expression system in which recombinant target genes were cotransfected into Vero cells together with intact activating genes. Plasmids containing cloned HSV-1 or HSV-2 immediate-early (IE) genes stimulated by up to 100-fold the expression from recombinant constructs containing the bacterial chloramphenicol acetyltransferase (CAT) gene under the control of the DE promoter/regulatory region from the genes for an HSV-2 38,000-molecular-weight (38K) protein and the HSV-1 thymidine kinase. This activation was specific to hybrid genes containing DE regulatory regions since no significant increases in expression were observed in cotransfection experiments with the CAT gene without any promoter region or under the control of a number of other regulatory regions, including an HSV-1 IE regulatory region, the complete or enhancerless early regulatory region of simian virus 40, and an inducible cellular promoter/regulatory region. By using a variety of cotransfected plasmids containing individual or different combinations of HSV-1 or HSV-2 IE genes, we show that of the five known IE genes, two, those coding for the 175K and 110K polypeptides, each possessed the ability to stimulate expression from both DE promoters. Cleavage of the input plasmids within the known coding regions for the 175K and 110K proteins abolished stimulation of DE/CAT gene expression, whereas cleavage outside the coding regions had no effect on stimulation. We conclude that stimulation of CAT expression occurred exclusively by a transactivation mechanism in which the products encoded by these IE genes acted on the DE hybrid constructs at the transcription level. No transcriptional stimulatory function was demonstrated for the IE 68K and 63K proteins, although our results indicate that the IE 12K protein may augment the DE stimulatory activity of the 175K and 110K proteins.