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

Role of the Herpes Simplex Virus CVSC Proteins at the Capsid Portal Vertex

The packaging of DNA into preformed capsids is a critical step during herpesvirus infection. For herpes simplex virus, this process requires the products of seven viral genes: the terminase proteins pUL15, pUL28, and pUL33; the capsid vertex-specific component (CVSC) proteins pUL17 and pUL25; and the portal proteins pUL6 and pUL32. The pUL6 portal dodecamer is anchored at one vertex of the capsid by interactions with the adjacent triplexes as well as helical density attributed to the pUL17 and pUL25 subunits of the CVSC. To define the roles and structures of the CVSC proteins in virus assembly and DNA packaging, we isolated a number of recombinant viruses expressing pUL25, pUL17, and pUL36 fused with green or red fluorescent proteins as well as viruses with specific deletions in the CVSC genes. Biochemical and structural studies of these mutants demonstrated that (i) four of the helices in the CVSC helix bundle can be attributed to two copies each of pUL36 and pUL25, (ii) pUL17 and pUL6 are required for capsid binding of the terminase complex in the nucleus, (iii) pUL17 is important for determining the site of the first cleavage reaction generating replicated genomes with termini derived from the long-arm component of the herpes simplex virus 1 (HSV-1) genome, (iv) pUL36 serves no direct role in cleavage/packaging, (v) cleavage and stable packaging of the viral genome involve an ordered interaction of the terminase complex and pUL25 with pUL17 at the portal vertex, and (vi) packaging of the viral genome results in a dramatic displacement of the portal.IMPORTANCE Herpes simplex virus 1 (HSV-1) is the causative agent of several pathologies ranging in severity from the common cold sore to life-threatening encephalitic infection. A critical step during productive HSV-1 infection is the cleavage and packaging of replicated, concatemeric viral DNA into preformed capsids. A key knowledge gap is how the capsid engages the replicated viral genome and the subsequent packaging of a unit-length HSV genome. Here, biochemical and structural studies focused on the unique portal vertex of wild-type HSV and packaging mutants provide insights into the mechanism of HSV genome packaging. The significance of our research is in identifying the portal proteins pUL6 and pUL17 as key viral factors for engaging the terminase complex with the capsid and the subsequent cleavage, packaging, and stable incorporation of the viral genome in the HSV-1 capsid.

Reactivation and Lytic Replication of Kaposi's Sarcoma-Associated Herpesvirus: An Update

The life cycle of Kaposi’s sarcoma-associated herpesvirus (KSHV) consists of two phases, latent and lytic. The virus establishes latency as a strategy for avoiding host immune surveillance and fusing symbiotically with the host for lifetime persistent infection. However, latency can be disrupted and KSHV is reactivated for entry into the lytic replication. Viral lytic replication is crucial for efficient dissemination from its long-term reservoir to the sites of disease and for the spread of the virus to new hosts. The balance of these two phases in the KSHV life cycle is important for both the virus and the host and control of the switch between these two phases is extremely complex. Various environmental factors such as oxidative stress, hypoxia, and certain chemicals have been shown to switch KSHV from latency to lytic reactivation. Immunosuppression, unbalanced inflammatory cytokines, and other viral co-infections also lead to the reactivation of KSHV. This review article summarizes the current understanding of the initiation and regulation of KSHV reactivation and the mechanisms underlying the process of viral lytic replication. In particular, the central role of an immediate-early gene product RTA in KSHV reactivation has been extensively investigated. These studies revealed multiple layers of regulation in activation of RTA as well as the multifunctional roles of RTA in the lytic replication cascade. Epigenetic regulation is known as a critical layer of control for the switch of KSHV between latency and lytic replication. The viral non-coding RNA, PAN, was demonstrated to play a central role in the epigenetic regulation by serving as a guide RNA that brought chromatin remodeling enzymes to the promoters of RTA and other lytic genes. In addition, a novel dimension of regulation by microPeptides emerged and has been shown to regulate RTA expression at the protein level. Overall, extensive investigation of KSHV reactivation and lytic replication has revealed a sophisticated regulation network that controls the important events in KSHV life cycle.

Polarized DNA ejection from the herpesvirus capsid

Ejection of DNA from the capsid is an early step in infection by all herpesviruses. Ejection or DNA uncoating occurs after a parental capsid has entered the host cell cytoplasm, migrated to the nucleus, and bound to a nuclear pore. DNA exits the capsid through the portal vertex and proceeds by way of the nuclear pore complex into the nucleoplasm where it is transcribed and replicated. Here, we describe use of an in vitro uncoating system to determine which genome end exits first from the herpes simplex virus 1 capsid. Purified DNA-containing capsids were bound to a solid surface and warmed under conditions in which some, but not all, of the DNA was ejected. Restriction endonuclease digestion was then used to identify the genomic origin of the ejected DNA. The results support the view that the S segment end exits the capsid first. Preferential release at the S end demonstrates that herpesvirus DNA uncoating conforms to the paradigm in double-stranded DNA bacteriophage where the last end packaged is the first to be ejected. Release of herpes simplex virus 1 DNA beginning at the S end causes the first gene to enter the host cell nucleus to be alpha4, a transcription factor required for expression of early genes.

Regulation of herpes simplex virus gene expression

Expression of the more than 80 individual genes of herpes simplex virus 1 (HSV-1) takes place in a tightly regulated sequential manner that was first described over 20 years ago. Investigations since that time have focused on understanding the mechanisms that regulate this orderly and efficient expression of viral genes. This review examines recent findings that have shed light on how this process is regulated during productive infection of the cell. Although the story is still not complete, several aspects of HSV gene expression are now clearer as a result of these findings. In particular, several new functions have recently been ascribed to some of the known viral regulatory proteins. The results indicate that the viral gene expression is regulated through transcriptional as well as post-transcriptional mechanisms. In addition, it has become increasingly clear that the virus has evolved specific functions to interact with the host cell in order to divert and redirect critical host functions for its own needs. Understanding the interactions of HSV and the host cell during infection will be essential for a complete understanding of how viral gene expression is regulated. Future challenges in the field will be to develop a complete understanding of the mechanisms that temporally regulate virus gene expression, and to identify and characterize the relevant interactions between the virus and the distinctive cell types normally infected by the virus.

Herpes simplex virus 1 ICP27 is required for transcription of two viral late (gamma 2) genes in infected cells

The herpes simplex virus infected cell protein 27 (ICP27) is required for the expression of certain early viral proteins and for many late proteins during productive infection. Expression of at least one late (gamma 2) gene, that encoding glycoprotein C, is severely restricted in the absence of functional ICP27. The exact mode of action by which ICP27 induces late gene expression is not known, but the effect is apparent at the mRNA level as demonstrated by Northern blot analysis. To determine whether ICP27 activates late genes via transcriptional or posttranscriptional mechanisms, we initially used nuclear run-on assays to measure transcription of viral genes in Vero cells infected with wild-type (WT) virus or an ICP27 nonsense mutant virus, n504. We observed a 4-fold reduction in the nuclear run-on signal from the coding strand of the gC gene for n504-infected cells compared to that of WT-infected cells. However, interpretation of the results was complicated by the observation of a significant signal from the noncoding strand in these experiments. To obviate the problem of symmetrical transcription, we utilized in vivo RNA pulse-labeling to measure the amount of transcription of viral genes in cells infected with either WT virus or n504 virus. We found a 5- to 10-fold reduction in the transcription of the gC and U(L)47 genes, two late genes, in cells infected with n504 compared to that in cells infected with WT virus. In contrast, transcription of the ICP8 gene, an early gene, was similar in WT and n504 virus-infected cells. We also examined the stability of the gC and U(L)47 gene transcripts in n504-infected cells, and we found it to be comparable to that in WT virus-infected cells, further supporting an effect on transcription. Transcription of the gC and U(L)47 genes by n504 was normal in a cell line that expresses WT ICP27. From these results we conclude that ICP27 is required for transcription of the late gC and U(L)47 genes during productive infection.

On the control of late gene expression in Kaposi's sarcoma-associated herpesvirus (human herpesvirus-8)

Herpesvirus late genes require viral DNA replication for maximal expression. Although late gene expression appears to require DNA replication in cis in alphaherpesviruses, studies in Epstein-Barr virus (EBV) suggest that this cis-requirement might not pertain to the gammaherpesviruses. Based on these findings, a system was created to investigate the elements required for the regulation of Kaposi's sarcoma-associated herpesvirus (KSHV; human herpesvirus-8) late gene expression. The transcript of a classic late gene encoding the viral assembly protein was characterized and reporter genes driven by the assembly protein promoter region were constructed. Unlike the EBV case, expression of a reporter gene under the control of the assembly protein promoter did not display authentic regulation when removed from the context of the viral genome. Although reporter expression rose in cells displaying lytic replication, this expression was not diminished by specific inhibitors of viral DNA synthesis. Minimal core promoters were similarly unable to reproduce late gene regulation. These results suggest that proper KSHV late gene expression is likely to be dependent upon virus lytic replication in cis and indicate that the regulation of KSHV late genes more closely resembles that observed in herpes simplex virus than that described for EBV.

Herpes simplex virus 1 late gene expression is preferentially inhibited during infection of the TAF250 mutant ts13 cell line

A key component of the polymerase II transcription machinery is the transcription factor TFIID, a complex that contains the TATA-box binding protein and several (10-12) associated factors designated as TAFs (TBP-associated factors). ts13 cells, which contain a temperature-sensitive mutant in TAF250, the largest subunit of TFIID, exhibit promoter-specific defects in gene expression at the nonpermissive temperature, suggesting that individual TAFs are required for transcription of specific subsets of eukaryotic genes. Herpes simplex virus 1 (HSV-1) does not replicate in ts13 cells at the nonpermissive temperature, but the point at which the replicative process is blocked is not known. We used the TAF250 defect in ts13 cells to investigate the role of TAF250 in the expression of HSV-1 genes of each temporal class. At a low m.o.i., expression of most immediate-early mRNAs is reduced at the nonpermissive temperature, and consequently, there is little expression of early genes and no viral DNA replication. In contrast, at high m.o.i., expression of immediate-early genes is unaffected by the TAF250 defect and is not dependent on de novo viral protein synthesis. Early genes and early proteins are produced under these conditions, and viral DNA replication ensues, albeit at somewhat reduced levels. In contrast, late gene expression and late protein synthesis are severely restricted, even in the presence of appreciable viral DNA replication. Thus the lack of late protein synthesis is responsible for the inability of HSV-1 to replicate in ts13 cells at the nonpermissive temperature. Further, it appears that late viral gene expression may be preferentially inhibited by the TAF250 mutation in ts13 cells.

Characterization of the initiator and downstream promoter elements of herpes simplex virus 1 late genes

Previously identified cis-acting regulatory elements of herpes simplex virus (HSV) 1 late promoters include a TATA element upstream from the start of transcription, an initiator-like element at the start of transcription, and sequences downstream from the start of transcription. To determine whether these elements are functionally equivalent to similar elements from other eukaryotic genes, model late promoters were constructed using well-characterized regulatory elements from non-HSV genes. These modular promoters were then inserted into the viral genome upstream from a lacZ marker gene. Results showed that a eukaryotic initiator element, along with a TATA element, can function as a late HSV promoter. Several initiator sequences from both viral and nonviral genes were functionally similar to the initiator-like element in HSV-1 late promoters; however, a random sequence of the same size and a similarly located sequence from the HSV-1 early thymidine kinase promoter could not substitute for the initiator element. These results indicate that eukaryotic initiator elements are functionally equivalent to HSV-1 late promoter initiator elements. In addition, the downstream element of the late glycoprotein C promoter was further analyzed by construction of a series of small deletions and insertions. The presence of the downstream glycoprotein C region in a promoter consisting of a strong TATA and initiator element increased mRNA expression by a modest amount; this effect appeared to be sequence specific and dependent on its exact alignment with the upstream elements of the promoter.

A block in glycoprotein processing correlates with small plaque morphology and virion targetting to cell-cell junctions for an oral and an anal strain of herpes simplex virus type-1

The characteristics of two clinical isolates of HSV-1 obtained from an oral (424) and an anal (490) lesion were compared with the highly passaged KOS strain. In contrast to KOS, the clinical isolates produced small plaques, were more cell-associated and the predominant viral glycoprotein species for gC and gD in infected cell lysates was the precursor, high mannose glycoform. Total virus production in Vero cells was equivalent for the three virus strains in one-step growths. Pulse-chase studies of glycoprotein C processing showed a reduction in rate at 7.5 h post infection and a significant block in processing at 10.5 h post infection for 424 and 490 but not KOS. Similar results were obtained for gD. The significant reduction in glycoprotein processing for 424 and 490 suggests a block in transport of viral glycoproteins or virions to and through the Golgi apparatus. Extracellular virions and the cell surface, prior to cell lysis, contained the processed gC glycoform suggesting a competent cellular glycan processing system. Upon co-infection of 424 or 490 with KOS or a gC- KOS strain, gC was processed to levels equivalent to KOS indicating that 424 and 490 are not inhibitory but that an activity(s) encoded by KOS facilitates maturation of gC from 424 and 490. Unlike KOS infected Vero cells, virion-containing vacuoles were observed in the cytoplasm at 12 h p.i. and extracellular virions were concentrated at cell-cell junctions of 424 or 490 infected cells but not in the perinuclear region. These results suggest that intracellular transport of viral glycoproteins and virions in 424 and 490 infected cells is different from KOS infected cells. The reduced level of viral glycoprotein maturation, virus release, cell surface presence and presence of virions at cell-cell junctions are consistent with small plaque production in tissue culture cells.

Arginine-rich regions succeeding the nuclear localization region of the herpes simplex virus type 1 regulatory protein ICP27 are required for efficient nuclear localization and late gene expression

The herpes simplex virus type 1 (HSV-1) immediate-early protein ICP27 is an essential regulatory protein that localizes to the nuclei of infected cells. The strong nuclear localization signal (NLS) of ICP27 was identified recently and shown to reside in the amino-terminal portion of the polypeptide from residues 110 to 137 (W.E. Mears, V. Lam, and S.A. Rice, J. Virol. 69:935-947, 1995). There are also two arginine-rich regions directly succeeding the NLS. The first of these arginine-rich sequences (residues 141 to 151), together with the NLS, has been shown by Mears et al. to form the nucleolar localization signal. Arginine-rich motifs are common in domains involved in nuclear localization and RNA binding. To analyze the role of the arginine-rich regions in ICP27, we constructed stably transformed cell lines containing ICP27 mutants with deletions of all or parts of the NLS and arginine-rich regions. We also constructed mutants in which these regions were replaced with heterologous NLSs or RNA-binding domains. Characterization of these mutants indicated that the arginine-rich regions were required but not sufficient for wild-type localization of ICP27. More importantly, the NLS and arginine-rich regions were also essential to the function of ICP27. Mutants lacking these sequences were defective in late gene expression during infection even when ICP27 was properly localized to the nucleus by substitution of the NLS from simian virus 40 large T antigen. Further, the defect in late gene expression could not be overcome by replacement with the highly basic RNA-binding domain of human immunodeficiency virus type 1 Tat. The deficiency in late gene expression was independent of ICP27's role in stimulating viral DNA replication. In addition, localization of the HSV-1 proteins ICP4, ICP0, and ICP8 was unaffected by ICP27 mutants in this region. These results suggest that the arginine-rich regions are required for efficient nuclear localization and for the regulatory activity of ICP27 involved in viral late gene expression.

Herpes simplex virus recombination vectors designed to allow insertion of modified promoters into transcriptionally "neutral" segments of the viral genome

The use of recombinant viruses has been essential in investigation of the biology of herpes simplex virus (HSV). In this communication we describe a number of viral recombination vectors that we have generated for use in promoter structure/function analysis within the context of the HSV-1 genome. We have utilized two regions of the HSV genome that contain genes nonessential for replication in cultured cells--the glycoprotein C (gC or UL44) locus in the UL of the genome and the area encompassing the promoter and 5' portion of the latency associated transcript (LAT) within the RL factual influence on promoters due to the site of insertion. Two different kinetic promoters were analyzed, those controlling expression of the gamma UL 38 and the beta dUTPase genes, in both loci. All constructs tested displayed reporter gene mRNA expression with expected kinetics, and we conclude that there are no neighboring cryptic promoter elements that could interfere with expression studies using the vectors described.

The herpes simplex virus type 1 major capsid protein (VP5-UL19) promoter contains two cis-acting elements influencing late expression

The herpes simplex virus type 1 (HSV-1) major capsid protein VP5 gene (UL19) is expressed with beta gamma (gamma 1 [leaky late]) kinetics. We have previously described the construction of recombinant HSV-1 in which the VP5 promoter was engineered to control the expression of the bacterial beta-galactosidase gene as a reporter (C.-J. Huang, S. A. Goodart, M. K. Rice, J. F. Guzowski, and E. K. Wagner, J. Virol. 67:5109-5116, 1993). Here we describe further mutational analysis in recombinant viruses. We have precisely defined the boundaries of the VP5 promoter and identified two regions important for both the level and the kinetics of expression. The 5' boundary was located at -48 relative to the initiation site of transcription by analyzing a series of nested deletions in the upstream sequence, and although a number of cis-acting sites influencing transient expression have been identified upstream of this point, these sites have no role in promoter activity during productive infection. Deletion of an Sp1-binding site located between -48 and the TATA box at -30 greatly reduced VP5 promoter activity late but not early after infection. A cis-acting element whose sequence resembles the human immunodeficiency virus type 1 initiator was located between -2 and +10 in the VP5 sequence by characterizing a series of deletions and site-directed block mutations downstream the TATA box. This element defines the 3' limit of the VP5 promoter, and like the upstream element, disruption of this element also inhibited promoter activity late in the productive cycle.

Characterization of the large tegument protein (ICP1/2) of herpes simplex virus type 1

ICP1/2 (also designated VP1/2) is a 270-kDa structural protein of herpes simplex virus type 1 (HSV-1) which is located in the tegument region of the virion. In this report we describe the production of a polyclonal antiserum specific for ICP1/2 and the use of this antiserum to examine the synthesis, processing, and intracellular localization of the viral polypeptide. Pulse-labeling studies indicated that ICP1/2 is synthesized late during infection, being initially detectable between 8 and 9 hr postinfection with the rate of synthesis continuing to increase until 11 to 12 hr postinfection. Further studies on the expression of ICP1/2 in the presence or absence of viral DNA replication indicated that the synthesis of the polypeptide is absolutely dependent on viral DNA replication. These results suggest that ICP1/2 represents a gamma 2 (true late) gene product. Additionally, we have performed experiments to determine if ICP1/2 is post-translationally modified in HSV-infected cells. These studies indicated that ICP1/2 is phosphorylated on serine residues; however, we found no evidence to suggest that the protein is glycosylated. Using subcellular fractionation and indirect immunofluorescence techniques, we have determined that ICP1/2 is diffusely distributed throughout the nucleus and cytoplasm of HSV-infected cells with no specific compartmentalization of the polypeptide.

Baculovirus expressed herpes simplex virus type 1 glycoprotein C protects mice from lethal HSV-1 infection

A recombinant baculovirus (vAc-gC1) was constructed that expresses the glycoprotein C (gC) gene of herpes simplex virus type 1 (HSV-1). When Sf9 cells were infected with this recombinant, a protein that was smaller in size than authentic HSV-1 gC was detected by Western blotting using anti-gC polyclonal antibody. The recombinant gC was susceptible to tunicamycin, partially resistant to Endo-H, and was found on the membrane of Sf9 cells. Antibodies raised in mice to recombinant gC reacted with gC from HSV-1 infected cells and neutralized the infectivity of HSV-1 in vitro. Immunized mice were protected from lethal challenge with HSV-1.

A detailed analysis of transcripts mapping to varicella zoster virus gene 14 (glycoprotein V)

We have characterized in detail those transcripts mapping to the varicella zoster virus (VZV) glycoprotein V (gpV) open reading frame (ORF). The analyses revealed that a major 1.95-kb and a minor 2.5-kb transcript map to these sequences for VZV strain Scott, with 1.8- and 2.3-kb transcripts in a vaccine Oka strain, consistent with intragenic repeat (R2) copy number differences. The transcripts for each strain are 5' coterminal, are polyadenylated, and do not seem to be spliced. Upstream of the cap site there are few obvious regulatory consensus sequences, but there is a potential CCAAT box at -59 bp and an unusual sequence at -25 to -33, ATTTAAATT, which may serve as the TATA box for this gene. The 3' termini map 10 to 20 bases downstream from potential polyadenylation signals: ATAAA for the 1.95-kb transcript and ACGTAAA for the 2.5-kb transcript. This transcript pattern is quite different from that observed for the gpV homologue in herpes simplex virus (HSV-1), glycoprotein C (gC). Strain Scott synthesizes about 20-fold more gpV-specific transcripts than a strain of the Oka vaccine virus, reflecting the amounts of gpV polypeptide accumulating in both strains; this implies that the defect in Oka gpV polypeptide production is at the level of transcription.

Overexpression in bacterial and identification in infected cells of the pseudorabies virus protein homologous to herpes simplex virus type 1 ICP18.5

The ICP18.5 gene (UL28) of herpes simplex virus type 1 is a member of a well-conserved gene family among herpesviruses and is thought to play a role in localization of viral glycoproteins. We have cloned, sequenced, and expressed the entire pseudorabies virus (PRV) ICP18.5 open reading frame in Escherichia coli as a Cro-ICP18.5 fusion protein. Rabbit antiserum against Cro-ICP18.5 immunoprecipitated a 79-kDa protein from PRV-infected cells as well as a 79-kDa protein from in vitro translation of a T7 RNA polymerase transcript of the ICP18.5 gene. ICP18.5 could be detected in infected cells by 2 h postinfection. Analysis by indirect immunofluorescence demonstrated that ICP18.5 became associated with the nucleus. Subcellular fractionation confirmed that ICP18.5 synthesized during a pulse-chase experiment appeared in the nuclear fraction with time and was stable for at least 2.5 h after synthesis. Pulse-chase analysis revealed that ICP18.5 was synthesized as a monomer during a 2-min pulse labeling but formed faster sedimenting complexes which were sensitive to sodium dodecyl sulfate (SDS) treatment. The majority of ICP18.5 appeared in complexes with an antigenically unrelated 70-kDa protein. Immunoblot analysis of total infected-cell extracts using polyvalent anti-ICP18.5 serum demonstrated that a 74-kDa cellular protein in addition to the 79-kDa ICP18.5 was detected. This cellular protein was present at similar levels in uninfected cells and in PRV-infected cells at least 12 h into the infectious cycle.

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

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

Isolation of a herpes simplex virus type 1 mutant deleted for the essential UL42 gene and characterization of its null phenotype

We isolated a cell line, designated V9, stably transformed with the herpes simplex virus type 1 (HSV-1) UL42 gene, which is one of seven genes required in trans for the replication of plasmids containing an HSV origin of replication (C. A. Wu, N. J. Nelson, D. J. McGeoch, and M. D. Challberg, J. Virol. 62:435-443, 1988). V9 cells inducibly expressed the product of the UL42 gene, the 65-kDa DNA-binding protein (65KDBP), and were used as a permissive host to construct a mutant virus deleted for this essential gene. The UL42 deletion mutant, designated Cgal delta 42, displayed a tight early phenotype in nonpermissive Vero cells producing no infectious progeny, viral DNA, or late gene products but accumulated selected immediate-early and early transcripts with kinetics similar to those of wild-type virus. Wild-type levels of viral DNA and infectious progeny were produced in permissive V9 cells, despite the fact that V9 cells infected with Cgal delta 42 accumulated less than 1% of the UL42 RNA and protein found in Cgal+ virus-infected V9 or Vero cells. These results indicate that only small quantities of the 65KDBP are required for the synthesis of HSV DNA and the production of infectious virus. Although we could find no evidence that the superinduction of the 65KDBP in V9 cells infected with Cgal+ repressed expression of HSV-1 genes as observed in cells expressing another DNA-binding protein, ICP8 (P. K. Orberg and P. A. Schaffer, J. Virol. 61:1136-1146, 1987), the induction of the 65KDBP in V9 cells correlated with an approximately 2-h-earlier shift in the expression of genes from all three kinetic classes. The availability of the UL42 mutant should facilitate the construction of more subtle UL42 mutants which will be useful in the elucidation of the interrelationship between the 65KDBP and other DNA replication proteins as well as in the characterization of additional important functional domains.

Differential regulation of endogenous and transduced beta-globin genes during infection of erythroid cells with a herpes simplex virus type 1 recombinant

We infected murine erythroleukemia cells with a nondefective herpes simplex virus (HSV) type 1 recombinant bearing the rabbit beta-globin gene under the control of its own promoter, in order to compare the regulation of a cellular gene residing in the viral genome to that of its active endogenous counterpart. We found that the viral globin gene was activated by HSV immediate-early polypeptides, whereas expression of the endogenous beta-globin gene was strongly suppressed: transcription was greatly inhibited, and beta-globin mRNA was rapidly degraded. Degradation of globin mRNA was induced by a component of the infecting virion and required a functional UL41 gene product. These results demonstrate that HSV products can have opposing effects on the expression of homologous genes located in the cellular and viral genomes and suggest that the preferential expression of HSV genes that occurs during infection is not achieved solely through sequence-specific differentiation between viral and cellular promoters or mRNAs.

Serologic type conversion of a herpes simplex virus type 1 (HSV-1) to an HSV-2 epitope caused by a single amino acid substitution in glycoprotein C

A monoclonal antibody to herpes simplex virus type 2 glycoprotein C (gC-2) did not recognize wild-type herpes simplex virus type 1 gC (gC-1) but did recognize a mutant gC-1 molecule. This conversion from a type 1 to a type 2 epitope was shown to be due to a single amino acid substitution in gC-1.

Characterization of the antigenic structure of herpes simplex virus type 1 glycoprotein C through DNA sequence analysis of monoclonal antibody-resistant mutants

Earlier studies of a group of monoclonal antibody-resistant (mar) mutants of herpes simplex virus type 1 glycoprotein C (gC) operationally defined two distinct antigenic sites on this molecule, each consisting of numerous overlapping epitopes. In this report, we further define epitopes of gC by sequence analysis of the mar mutant gC genes. In 18 mar mutants studied, the mar phenotype was associated with a single nucleotide substitution and a single predicted amino acid change. The mutations were localized to two regions within the coding sequence of the external domain of gC and correlated with the two previously defined antigenic sites. The predicted amino acid substitutions of site I mutants resided between residues Gln-307 and Pro-373, whereas those of site II mutants occurred between amino acids Arg-129 and Glu-247. Of the 12 site II mutations, 9 induced amino acid substitutions within an arginine-rich segment of 8 amino acids extending from residues 143 to 151. The clustering of the majority of substituted residues suggests that they contribute to the structure of the affected sites. Moreover, the patterns of substitutions which affected recognition by antibodies with similar epitope specificities provided evidence that epitope structures are physically linked and overlap within antigenic sites. Of the nine epitopes defined on the basis of mutations, three were located within site I and six were located within site II. Substituted residues affecting the site I epitopes did not overlap substituted residues of site II, supporting our earlier conclusion that sites I and II reside in spatially distinct antigenic domains. A computer analysis of the distribution of charged residues and the predicted secondary structural features of wild-type gC revealed that the two antigenic sites reside within the most hydrophilic regions of the molecule and that the antigenic residues are likely to be organized as beta sheets which loop out from the surface of the molecule. Together, these data and our previous studies support the conclusion that the mar mutations identified by sequence analysis very likely occur within or near the epitope structures themselves. Thus, two highly antigenic regions of gC have now been physically and genetically mapped to well-defined domains of the protein molecule.

Expression of the herpes simplex virus type 1 glycoprotein C gene requires sequences in the 5' noncoding region of the gene

The role of the 5' noncoding region of the herpes simplex virus type 1 glycoprotein C (gC) gene in viral gene expression was investigated with recombinant herpesviruses that contained the bacterial beta-galactosidase gene under the control of the gC promoter-regulatory region. Each of these viruses had the same DNA sequences from the start of gC transcription upstream to -114 but had variable segments of the downstream 140-base-pair sequence that is between the start of gC transcription and translation. Analysis of beta-galactosidase expression and mRNA synthesis from these viruses demonstrated the importance of DNA sequences from the start of gC transcription downstream to +38 for optimal expression from the gC promoter.

The influence of the herpes simplex virus-1 DNA template environment on the regulation of gene expression

To determine the role of the HSV-1 genome structure and environment on the regulation of gene expression, we constructed recombinant viruses containing a heterologous gene inserted into either the immediate early ICPO or late glycoprotein C (gC) genes of HSV-1. The heterologous gene consisted of the SV40 early promoter (without enhancer sequences) linked to the coding sequences for the bacterial chloramphenicol acetyl transferase (CAT). The expression of CAT was examined in Vero cells infected with either virus (named ICP0-CAT and Sph 6). For both recombinants, expression of CAT was not dependent upon prior viral protein synthesis. The kinetics of expression of CAT-specific mRNA resembled that of the HSV-1 genes into which CAT was inserted. Primer extension analysis revealed that the SV40 promoter is recognized and used when placed in cis in two different HSV-1 genome locations, and Northern hybridization experiments confirmed that the heterologous gene was expressed in the absence of prior viral protein synthesis. Therefore, this gene was not regulated as strictly as an HSV-1 gene, but was influenced by the environment into which it was placed, presumably by factors that are present when the normal viral gene is on.

Herpes simplex virus alpha protein ICP27 can inhibit or augment viral gene transactivation

Three of the five alpha (immediate early) gene products of herpes simplex virus, infected cell proteins (ICPs) 4, 0, and 27 play a role in the control of expression of viral beta (delayed-early) and gamma (late) genes. We report here that ICP27 can inhibit or augment the individual or combined abilities of ICP4 and ICP0 to stimulate expression of chimeric genes containing viral gene promoters in a transient expression system. The specific effect of ICP27 was dependent on the viral gene promoter in the chimeric gene. ICP27 inhibited the ability of ICP4 and ICP0 to activate some beta gene promoters but augmented their ability to activate other beta or gamma 1 gene promoters when they were used in the target genes. Activation of the target genes by adenovirus E1A was not affected by ICP27 under the same conditions. ICP27 also repressed the ability of ICP0 to stimulate expression of a chimeric gene containing an alpha gene promoter. Insertion of a termination codon in the middle of the ICP27 coding region severely reduced the inhibitory effect of the plasmid, indicating that this activity requires expression of functional ICP27 polypeptide. This report focuses on the ICP27 activity that negatively regulates ICP4 transactivation of a chimeric gene containing the upstream sequences of the HSV beta gene ICP8. ICP27 decreased the level of mRNA initiated at the transcriptional start site of the ICP8 gene. The level of expression of the ICP4 gene was not changed by ICP27 but an alteration in the electrophoretic mobility of ICP4 expressed was observed. The modulatory effect of ICP27 on HSV transactivators may control the progress of the lytic cycle or provide a balance that varies in different cell types to affect whether lytic or latent infection ensues.

Transcriptional activation with concurrent or nonconcurrent template replication has differential effects on transient expression from herpes simplex virus promoters

We have used two methods to induce template replication in order to assess the effect on expression of marker genes controlled by herpes simplex virus type 1 (HSV-1) promoters. One method used the HSV-1 origin of DNA replication from the short repeat region of the viral genome (HSV-1 oris), and allowed simultaneous replication and transcriptional activation of the plasmid-borne template. The other, using the simian virus 40 origin of replication (SV40 ori) allowed plasmid template replication prior to activation of transcription by HSV-1 infection. The two regimes had markedly different effects upon the levels of reporter gene activity induced by HSV-1 superinfection. Replication of reporter plasmids using the SV40 ori yielded levels of reporter gene activity proportional to plasmid copy number when cells were superinfected with HSV-1. In contrast, our results indicated that sequences containing, or in close proximity to, the HSV-1 oris in the reporter plasmid had a significant inhibitory effect on expression from all viral promoters whether or not the plasmid was allowed to replicate. Still, the early (beta) promoter-controlled reporter enzyme activity declined at late times while that controlled by the strict late (gamma) promoter was significantly higher following HSV-1 oris-mediated template replication.

The role of viral and cellular nuclear proteins in herpes simplex virus replication

Following infection of cells by herpes simplex virus, the cell nucleus is subverted for transcription and replication of the viral genome and assembly of progeny nucleocapsids. The transition from host to viral transcription involves viral proteins that influence the ability of the cellular RNA polymerase II to transcribe a series of viral genes. The regulation of RNA polymerase II activity by viral gene products seems to occur by several different mechanisms: (1) viral proteins complex with cellular proteins and alter their transcription-promoting activity (e.g., alpha TIF), (2) viral proteins bind to specific DNA sequences and alter transcription (e.g., ICP4), and (3) viral proteins affect the posttranslational modification of viral or cellular transcriptional regulatory proteins (e.g., possibly ICP27). Thus, HSV may utilize several different approaches to influence the ability of host-cell RNA polymerase II to transcribe viral genes. Although it is known that viral transcription uses the host-cell polymerase II, it is not known whether viral infection causes a change in the structural elements of the nucleus that promote transcription. In contrast, HSV encodes a new DNA polymerase and accessory proteins that complex with and reorganize cellular proteins to form new structures where viral DNA replication takes place. HSV may encode a large number of DNA replication proteins, including a new polymerase, because it replicates in resting cells where these cellular gene products would never be expressed. However, it imitates the host cell in that it localizes viral DNA replication proteins to discrete compartments of the nucleus where viral DNA synthesis takes place. Furthermore, there is evidence that at least one specific viral gene protein can play a role in organizing the assembly of the DNA replication structures. Further work in this system may determine whether assembly of these structures is essential for efficient viral DNA replication and if so, why assembly of these structures is necessary. Thus, the study of the localization and assembly of HSV DNA replication proteins provides a system to examine the mechanisms involved in morphogenesis of the cell nucleus. Therefore, several critical principles are apparent from these discussions of the metabolism of HSV transcription and DNA replication. First, there are many ways in which the activity of RNA polymerase II can be regulated, and HSV proteins exploit several of these in controlling the transcription of a single DNA molecule. Second, the interplay of these multiple regulatory pathways is likely to control the progress of the lytic cycle and may play a role in determining the lytic versus latent infection decision.(ABSTRACT TRUNCATED AT 400 WORDS)

Promoter sequence and cell type can dramatically affect the efficiency of transcriptional activation induced by herpes simplex virus type 1 and its immediate-early gene products Vmw175 and Vmw110

The activation of transcription of the early and late classes of viral genes during infection by herpes simplex virus type 1 (HSV-1) requires the prior expression of immediate-early (IE) gene products. The IE gene products can also activate certain cellular and heterologous viral promoters. This paper presents a thorough analysis of transactivation of the HSV-1 glycoprotein gD and simian virus 40 early promoters, and two other promoters that are hybrids of both, under a variety of experimental conditions. Two methods of transactivation (superinfection with virus and co-transfection with isolated IE genes) have been used with all four target promoters in a variety of cell types. The conclusions are: (1) promoter sequence affects the efficiency of promoter activation by infectious HSV-1 virus, but this activation is not restricted to HSV promoters; (2) cell type affects the efficiency of promoter activation by HSV-1, and this can lead to a failure to activate a promoter in one cell type but not in others in which activation is generally more efficient; (3) a promoter can be activated to different extents in co-transfection experiments using plasmids carrying isolated IE genes that express Vmw110 or Vmw175 or when both are used together; (4) the pattern of activation of a promoter by the IE gene products in cotransfection experiments varies in different cell types; (5) changes in promoter sequence can alter the pattern of activation by the different IE polypeptides, and this pattern can again differ in different cell types; (6) other apparently minor experimental variables, as might exist between the standard methods used in different laboratories, can also affect the patterns of activation observed. The results are discussed in terms of the mechanism of action of the HSV-1 IE gene products and the limitations of the co-transfection assay.

The glycoprotein C gene of herpes simplex virus 1 resident in clonal L cell lines manifests two regulatory domains conferring a dominant B and a subordinate gamma 2 regulation

Earlier studies have shown that late, gamma 2, genes of herpes simplex virus 1 stably incorporated into the environment of the cell are regulated as beta genes. For example, the induction of the intact gene specifying glycoprotein C (gC) resident in a clonal L cell line superinfected with a gC- virus was enhanced in the presence of inhibitory concentrations of phosphonoacetate (PAA), a viral DNA synthesis inhibitor. Moreover, the gene was induced by superinfection at the nonpermissive temperature with tsHA1, a temperature-sensitive (ts) DNA- virus mutant. In the viral genome, the gC gene is not expressed by the tsHA1 mutant at the nonpermissive temperature or by the mutant or wild-type virus at the permissive temperature in the presence of inhibitory concentrations of PAA. We report that expression of a truncated gC gene introduced in the same fashion and resident in a clonal L cell line was at least partially sensitive to PAA and was not induced by tsHA1 at the nonpermissive temperature. The gene was transcribed from a prokaryotic transcription initiation site in the plasmid. Induction of gene expression by superinfecting virus did not result in appreciable amplification of the gene. We conclude that gC, a gamma 2 gene, contains two regulatory domains. The gene domain upstream from nucleotide +22 confers beta-like regulation, whereas the gene domain downstream from +22 confers gamma 2 regulation. In the gene resident in cells in culture the upstream regulatory domain is dominant, whereas the converse is true for the gene resident in the viral genome.

Activation of herpes simplex virus 1 gamma 2 genes by viral DNA replication

The expression of gamma 2 or true gamma genes resident in the herpes simplex virus 1 genome requires functional products of genes expressed earlier in infection and viral DNA synthesis. To determine whether the requirement for viral DNA synthesis for the expression of gamma 2 genes reflects a trans-acting function of a product of one or a few genes made or activated during viral DNA synthesis or whether it reflects a cis effect of DNA synthesis at specific sites, 143 thymidine kinase (TK) minus cells were sequentially infected with a virus carrying a 700-bp deletion of the TK gene and 6 hr later with wild-type or recombinant viruses carrying an alpha-TK or a gamma 2-TK gene in either the presence or absence of viral DNA synthesis. These experiments indicated that the gamma 2-TK gene contained in an unreplicated viral genome was not expressed by trans-acting factors specified before and during DNA synthesis by the first infecting virus, and, therefore, the induction of gamma 2 genes appears to be mediated by a cis-acting function associated with viral DNA synthesis.