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

A 77 Amino Acid Region in the N-Terminal Half of the HSV-1 E3 Ubiquitin Ligase ICP0 Contributes to Counteracting an Established Type 1 Interferon Response

Herpes simplex virus 1 (HSV-1) is a human pathogen capable of establishing lifelong latent infections that can reactivate under stress conditions. A viral immediate early protein that plays important roles in the HSV-1 lytic and latent infections is the viral E3 ubiquitin ligase, ICP0. ICP0 transactivates all temporal classes of HSV-1 genes and facilitates viral gene expression. ICP0 also impairs the antiviral effects of interferon (IFN)-β, a component of host innate defenses known to limit viral replication. To begin to understand how ICP0 allows HSV-1 to disarm the IFN-β response, we performed genetic analyses using a series of ICP0 truncation mutants in the absence and presence of IFN-β in cell culture. We observed that IFN-β pretreatment of cells significantly impaired the replication of the ICP0 truncation mutants, n212 and n312, which code for the first 211 and 311 amino acids of ICP0, respectively; this effect of IFN-β correlated with decreased HSV-1 early and late gene expression. This increased sensitivity to IFN-β was not as apparent with the ICP0 mutant, n389. Our mapping studies indicate that loss of 77 amino acids from residues 312 to 388 in the N-terminal half of ICP0 resulted in a virus that was significantly more sensitive to cells pre-exposed to IFN-β. This 77 amino acid region contains a phospho-SUMO-interacting motif or -SIM, which we propose participates in ICP0's ability to counteract the antiviral response established by IFN-β. IMPORTANCE Interferons (IFNs) are secreted cellular factors that are induced by viral infection and limit replication. HSV-1 is largely refractory to the antiviral effects of type 1 IFNs, which are synthesized shortly after viral infection, in part through the activities of the viral regulatory protein, ICP0. To understand how ICP0 impedes the antiviral effects of type 1 IFNs, we used a series of HSV-1 ICP0 mutants and examined their viral replication and gene expression levels in cells stimulated with IFN-β (a type 1 IFN). Our mapping data identifies a discrete 77 amino acid region in the N-terminal half of ICP0 that facilitates HSV-1 resistance to IFN-β. This region of ICP0 is modified by phosphorylation and binds to the posttranslational modification SUMO, suggesting that HSV, and potentially other viruses, may counteract type 1 IFN signaling by altering SUMO and/or SUMO modified cellular proteins.

The major tegument structural protein VP22 targets areas of dispersed nucleolin and marginalized chromatin during productive herpes simplex virus 1 infection

The herpes simplex virus (HSV) major tegument structural protein VP22 resides in multiple subcellular regions during productive infection. During an analysis of the molecular determinants of these localizations, we observed that a transfected fusion of the C-terminal portion of VP22, containing its pat4 nuclear localization signal, with GFP lacked nucleolar sparing compared to GFP alone. Thus, the initial goal was to determine whether VP22 associates with nucleoli. Using an optimized indirect immunofluorescence system to visualize nucleolin and viral proteins, we observed that VP22 present in VP22-expressing Vero (V49) cells "surrounded" nucleolin. These two initial findings implied that VP22 might associate directly with nucleoli. We next analyzed HSV-infected cells and observed that at late times, anti-nucleolin immune reactivity was dispersed throughout the nuclei while it retained uniform, circular staining in mock-infected cells. Time course infection experiments indicated that nucleolin initiated its transition from uniform to dispersed structures between 2 and 4 hpi. Comparison of Hoechst stained nuclei showed bright anti-nucleolin staining localized to regions of marginalized chromatin. These effects required de novo infected cell protein synthesis. A portion of VP22 detected in nuclei at 4 and 6 hpi localized to these areas of altered nucleolin and marginalized chromatin. VP22 was excluded from viral replication compartments containing the viral regulatory protein ICP22. Finally, altered nucleolin and marginalized chromatin were detected with a VP22-null virus, indicating that VP22 was not responsible for these nuclear architecture alterations. Thus, we conclude that nuclear VP22 targets unique subnuclear structures early (<6hpi) during herpes simplex virus 1 (HSV-1) infection.

Highly efficient regulation of gene expression by tetracycline in a replication-defective herpes simplex viral vector

Employing the tetracycline repressor tetR and the wild-type hCMV major immediate-early promoter, we have developed a highly sensitive tetracycline-inducible transcription switch in mammalian cells (T-REx; Invitrogen, Carlsbad, CA, USA). In view of the previous difficulty in achieving regulatable gene expression in recombinant HSV vector systems, we constructed a T-REx-encoding replication-defective HSV-1 recombinant, QR9TO-lacZ, that encodes two copies of the tetR gene controlled by the HSV-1 immediate-early ICP0 promoter and a reporter, the LacZ gene, under the control of the tetO-bearing hCMV major immediate-early promoter. Infection of cells, such as Vero, PC12, and NGF-differentiated PC12 cells, with QR9TO-lacZ led to 300- to 1000-fold tetracycline-regulated gene expression. Moreover, the expression of the LacZ gene by QR9TO-lacZ can be finely controlled by tetracycline in a dose-dependent fashion. Efficiently regulated gene expression can also be achieved in vivo following intracerebral and footpad inoculations in mice. The demonstrated capability of T-REx for achieving high levels of sensitively regulated gene expression in the context of the HSV-1 genome will significantly expand the utility of HSV-based vector systems for studying gene function in the nervous system and delivering regulated gene expression in therapeutic applications, particularly in the treatment of CNS diseases.

Differential cellular requirements for activation of herpes simplex virus type 1 early (tk) and late (gC) promoters by ICP4

The herpes simplex virus type 1 immediate-early protein, ICP4, activates the transcription of viral early and late genes and is essential for viral growth. It has been shown to bind DNA and interact with components of the general transcription machinery to activate or repress viral transcription, depending upon promoter context. Since early and late gene promoters have different architectures and cellular metabolism may be very different at early and late times after infection, the cellular requirements for ICP4-mediated activation of early and late genes may differ. This hypothesis was tested using tk and gC as representative early and late promoters, respectively. Nuclear extracts and phosphocellulose column fractions derived from nuclear extracts were able to reconstitute basal and ICP4-activated transcription of both promoters in vitro. When examining the contribution of the general transcription factors on the ability of ICP4 to activate transcription, the fraction containing the general transcription factor TFIIA was not essential for ICP4 activation of the gC promoter, but it was required for efficient activation of the tk promoter. The addition of recombinant TFIIA restored the ability of ICP4 to efficiently activate the tk promoter, but it had no net effect on activation of the gC promoter. The dispensability of TFIIA for ICP4 activation of the gC promoter required an intact INR element. In addition, microarray and Northern blot analysis indicated that TFIIA abundance may be reduced at late times of infection. This decrease in TFIIA expression during infection and its dispensability for activation of late but not early genes suggest one of possibly many mechanisms for the transition from viral early to late gene expression.

Herpes simplex virus type 1 origins of DNA replication play no role in the regulation of flanking promoters

Herpes simplex virus (HSV) exhibits altered gene regulation in neuronal compared to nonneuronal tissues. It has been hypothesized that initiation of DNA synthesis at the viral origins of replication (oriS and oriL) is a critical step in the upregulation of transcriptional activity of flanking divergent promoters, thereby increasing productive gene expression in neurons. Notably, oriS is flanked by the immediate-early (IE) ICP4 and ICP22/47 promoters, and oriL is flanked by the early (E) UL29 and UL30 promoters. To test this hypothesis further, a series of constructs were generated in which these promoters were placed upstream of luciferase genes. In addition, DNA replication origins were deleted in the context of these promoter constructs. All cassettes were recombined into the viral genome of HSV type 1 strain KOS at a site distal to its native origins. Recombinant reporter expression was monitored in vitro and in vivo to determine the role of viral origins of DNA replication in the regulation of their flanking promoters. Reporter gene expression was unaffected by the presence or absence of oriS or oriL, with the exception of a twofold increase in ICP22/47 promoter activity in the absence of oriS. DNA synthesis inhibitors resulted in a decrease of both IE- and E-promoter activity in primary cells but not continuous cell cultures. Reporter activity was readily assayed in vivo during acute infection and reactivation from latency and was also sensitive to DNA synthesis inhibitors. In all assays, reporter gene expression was unaffected by the presence or absence of either oriS or oriL. These data support the requirement of DNA synthesis for full viral gene expression in vivo but suggest that the origin elements play no role in the regulation of their flanking promoters.

The initiator element in a herpes simplex virus type 1 late-gene promoter enhances activation by ICP4, resulting in abundant late-gene expression

The start site regions of late genes of herpes simplex virus type 1 are similar to the eukaryotic initiator sequence (Inr), have been shown to affect the levels of expression, and may also play a role in transcription activation by the viral activator ICP4. A series of linker-scanning mutations spanning the start site of transcription and several downstream mutations in the true late gC promoter were analyzed in reconstituted in vitro transcription reactions with and without ICP4, as well as in the context of the viral genome during infection. The nucleotide contacts previously found to be important for Inr function were also found to be important for optimal induction by ICP4. While the Inr had a substantial effect on the accumulation of gC RNA during infection, no other sequence downstream of the TATA box to +124 had a significant effect on levels of expression during infection. Therefore, these studies suggest that TATA box and the Inr are the only cis-acting elements required to achieve optimal expression of gC, and that the high levels of late-gene transcription may be largely due to the induction by ICP4, functioning through the Inr element.

Multiple immediate-early gene-deficient herpes simplex virus vectors allowing efficient gene delivery to neurons in culture and widespread gene delivery to the central nervous system in vivo

Herpes simplex virus (HSV) has several potential advantages as a vector for delivering genes to the nervous system. The virus naturally infects and remains latent in neurons and has evolved the ability of highly efficient retrograde transport from the site of infection at the periphery to the site of latency in the spinal ganglia. HSV is a large virus, potentially allowing the insertion of multiple or very large transgenes. Furthermore, HSV does not integrate into the host chromosome, removing any potential for insertional activation or inactivation of cellular genes. However, the development of HSV vectors for the central nervous system that exploit these properties has been problematical. This has mainly been due to either vector toxicity or an inability to maintain transgene expression. Here we report the development of highly disabled versions of HSV-1 deleted for ICP27, ICP4, and ICP34.5/open reading frame P and with an inactivating mutation in VP16. These viruses express only minimal levels of any of the immediate-early genes in noncomplementing cells. Transgene expression is maintained for extended periods with promoter systems containing elements from the HSV latency-associated transcript promoter (J. A. Palmer et al., J. Virol. 74:5604-5618, 2000). Unlike less-disabled viruses, these vectors allow highly effective gene delivery both to neurons in culture and to the central nervous system in vivo. Gene delivery in vivo is further enhanced by the retrograde transport capabilities of HSV. Here the vector is efficiently transported from the site of inoculation to connected sites within the nervous system. This is demonstrated by gene delivery to both the striatum and substantia nigra following striatal inoculation; to the spinal cord, spinal ganglia, and brainstem following injection into the spinal cord; and to retinal ganglion neurons following injection into the superior colliculus and thalamus.

Distinct responses of the herpes simplex virus and varicella zoster virus immediate early promoters to the cellular transcription factors Brn-3a and Brn-3b

The related viruses herpes simplex virus (HSV) and varicella zoster virus (VZV) show distinct but related patterns of latent infection and reactivation in human sensory ganglia. The cellular POU family transcription factors Brn-3a and Brn-3b are expressed in sensory ganglia and bind to the TAATGARAT (R stands for purine) regulatory motifs in the immediate-early gene promoters of these viruses. We show that Brn-3a activates the full length HSV IE1 promoter whereas Brn-3b represses its activity. In contrast both Brn-3a and Brn-3b activate the full length VZV IE promoter. The response of the full length VZV promoter to Brn-3b is not observed with a minimal VZV immediate-early promoter lacking any TAATGARAT elements and cannot be restored by addition of either the upstream TAATGARAT-containing region of the HSV IE promoter or a VZV TAATGARAT-like element to this minimal promoter. The unique effect of Brn-3b on the full length VZV immediate early gene promoter may play a key role in the distinct pattern of latent infection and reactivation observed with this virus in vivo.

The ability of the inhibitory domain of the POU family transcription factor Oct-2 to interfere with promoter activation by different classes of activation domains is dependent upon the nature of the basal promoter elements

The Oct-2 transcription factor contains an inhibitory domain which is able to repress transcription following DNA binding. Here we show that within the neuronally expressed Oct-2.5 form, the inhibitory domain can strongly inhibit activation by transcription factor activation domains which are either composed predominantly of acidic residues or contain the HOB motif, whereas it has a weaker effect or no effect on proline-rich activation domains and on a glutamine-rich domain. In contrast, the isolated inhibitory domain of Oct-2 can efficiently repress all types of activation domains. This effect is observed however, only on TATA box-containing promoters and not on promoters containing an initiator motif. This widespread inhibition of different activation domains and its dependence on the nature of the basal promoter elements indicate that the inhibitory domain is likely to act by contacting a common downstream target of activation domains within the basal transcriptional complex bound at the TATA box rather than quenching specific activation domains by direct interaction. These effects are discussed in terms of the functional role of the inhibitory domain within Oct-2.5 and the mechanism by which it acts.

Repression of the alpha0 gene by ICP4 during a productive herpes simplex virus infection

During a productive infection by herpes simplex virus type 1 (HSV-1), ICP4, the major regulatory protein encoded by the alpha4 gene, binds to its transcription initiation site and represses the accumulation of alpha4 RNA. Evidence suggests that the degree of repression by ICP4 is a function of the absolute distance of an ICP4 binding site 3' from a TATA box. However, repression of HSV-1 gene expression by ICP4 through binding sites located 5' of TATA boxes, as in the case of the alpha0 gene, has not been adequately addressed. To this end, recombinant alpha0 promoters with various arrays of ICP4 binding sites flanking the alpha0 TATA box were constructed and recombined into the HSV-1 genome. Our results demonstrate the following. (i) Destruction of the endogenous alphaO ICP4 binding site, located 5' of the TATA box, results in derepression of alpha0 protein and RNA accumulation in infected Vero cells. (ii) The degree of alpha0 derepression is equivalent to that reported for the alpha4 gene following destruction of the ICP4 binding site at the alpha4 mRNA cap site in HSV-1. (iii) Introduction of an ICP4 binding site at the alpha0 mRNA cap site represses the accumulation of alpha0 RNA greater than threefold relative to the wild type. (iv) Changes in the abundance of alpha0 protein and RNA in infected cells do not affect replication or growth of HSV-1 in tissue culture. Our findings are consistent with the conclusion that alpha0 transcription is repressed by ICP4. These results demonstrate that repression by ICP4 can occur through binding sites located 5' of virus gene TATA boxes in HSV-1. Thus, models addressing repression of HSV-1 gene expression by ICP4 should incorporate the role of binding sites located 5', as well as 3', of virus gene TATA boxes.

Polyamines alter sequence-specific DNA-protein interactions

The polyamines are abundant biogenic cations implicated in many biological processes. Despite a plethora of evidence on polyamine-induced DNA conformational changes, no thorough study of their effects on the activities of sequence-specific DNA binding proteins has been performed. We describe the in vitro effects of polyamines on the activities of purified, representative DNA-binding proteins, and on complex protein mixtures. Polyamines at physiological concentrations enhance the binding of several proteins to DNA (e.g. USF, TFE3, Ig/EBP, NF-IL6, YY1 and ICP-4, a herpes simplex virus gene regulator), but inhibit others (e.g. Oct-1). The degree of enhancement correlates with cationic charge; divalent putrescine is ineffective whereas tetravalent spermine is more potent than trivalent spermidine. Polyamine effects on USF and ICP-4 result from increased rate of complex formation rather than a decreased rate of dissociation. DNAse I footprint analysis indicated that polyamines do not alter DNA-protein contacts. Polyamines also facilitate formation of complexes involving binding of more than one protein on a DNA fragment.

Activation of the herpes simplex virus immediate-early gene promoters by neuronally expressed POU family transcription factors

Herpes simplex virus immediate-early (IE) promoters contain the TAATGARAT motif which acts as a target site for the cellular POU family transcription factors Oct-1 and Oct-2. Here we show that other members of the POU family that are expressed in sensory neurons can also affect IE promoter activity. In particular, two members of the Brn-3 family of POU proteins Brn-3a and Brn-3c can activate the IE-1 and IE-3 promoters when co-transfected into fibroblasts and neuronal cells whereas a third member Brn-3b represses IE promoter activity. In contrast, Brn-3 proteins cannot overcome the inhibitory effect of neuronal Oct-2 on IE promoter activity in co-transfections nor do they prevent transactivation of the IE promoters by the Oct-1-Vmw65 complex. The potential regulation of the IE promoters by several different neuronally expressed POU proteins during the initiation, maintenance and re-activation of latent infection in sensory neurons is discussed.

Functional interaction between different isoforms of the Oct-2 transcription factor expressed in neuronal cells

The predominant neuronal isoforms of the Oct-2 transcription factor, Oct 2.4 and Oct 2.5, repress the herpes simplex virus immediate-early promoter both in neuronal cells and in fibroblasts normally lacking Oct-2. In contrast, the predominant B lymphocyte form Oct 2.1, which is present at a lower level in neuronal cells, activates the immediate-early promoter in fibroblasts but represses it in neuronal cells. We show here that both Oct 2.4 and Oct 2.5 can functionally interact with Oct 2.1 and convert it from an activator into a repressor. Hence, the cell type-specific activity of Oct 2.1 results from the presence of Oct 2.4 and 2.5 in neuronal cells and their absence in other cell types. The significance of this effect is discussed in terms of the role of Oct-2 in the regulation of viral and cellular gene expression in neuronal cells.

Binding sites for the herpes simplex virus immediate-early protein ICP4 impose an increased dependence on viral DNA replication on simple model promoters located in the viral genome

We examined the ability of binding sites for the herpes simplex virus immediate-early protein ICP4 to alter the regulation of closely linked promoters by placing strong ICP4 binding sites upstream or downstream of simple TATA promoters in the intact viral genome. We found that binding sites strongly reduced the levels of expression at early times postinfection and that this effect was partially overcome after the onset of viral DNA replication. These data confirm that DNA-bound ICP4 can inhibit the activity of a closely linked promoter and raise the possibility that ICP4 binding sites contribute to temporal regulation during infection.

Dispensable sequence motifs in the RAG-1 and RAG-2 genes for plasmid V(D)J recombination

As a probe of whether RAG-1 and RAG-2 gene products activate other genes or form part of the recombinase itself, certain mutants of the RAG genes were assayed for their ability to activate variable-diversity-joining region [V(D)J] recombination in a plasmid substrate in fibroblasts. The results indicate that the N-terminal one-third of RAG-1, including a zinc-finger-like domain, and an acidic domain of RAG-2 are dispensable for activating V(D)J recombination in a fibroblast, although they contribute quantitatively. In contrast, deletion of the C-terminal segment of RAG-1, which has homology to a topoisomerase-like protein from yeast, abolished recombination activation. These results do not support the hypothesis that the RAG gene products are transcription factors and suggest the possibility that they are parts of the recombination machinery.

The varicella-zoster virus immediate early protein, IE62, can positively regulate its cognate promoter

Varicella-Zoster virus (VZV) is a neurotropic alphaherpes virus closely related to herpes simplex virus (HSV). However, unlike its close relative HSV, VZV lacks a functional alpha-TIF (alpha-gene transinducing factor) that activates the transcription of immediate early genes during the initial events of the virus life cycle. Hence, in the absence of a functional alpha-TIF, the mechanism triggering the expression of immediate early genes in VZV at present remains unclear. Accumulating evidence indicates that the gene product of the putative immediate early gene ORF62 (IE62) plays a pivotal role in activating VZV genes of all three putative kinetic classes, namely immediate early (alpha), early (beta), and late (gamma) classes of VZV genes. In the present study, we show that IE62 can positively autoregulate its cognate promoter using a transient transfection assay, both in lymphocytes and in neural cells. In the same system, we can also demonstrate activation of the VZV IE62 promoter by HSV ICP4. By deletion analysis and oligonucleotide-directed site-specific mutagenesis we have localized specific regions in the IE62 promoter/upstream sequences that mediate inducibility by IE62 and HSV ICP4, and provide evidence that this promoter activation by these two proteins may be through different mechanisms. These data, taken together with the recent demonstration of the presence of IE62 in the VZ virion tegument (Kinchington, P.R., Hoagland, J.K., Arvin, A.M., Ruyechan, W.T., and Hay, J. 1992. J. Virol. 66, 359-366) provides a possible mechanism by which the triggering of VZV gene expression occurs in the absence of a functional alpha-TIF protein.

Analysis of the gB promoter of herpes simplex virus type 1: high-level expression requires both an 89-base-pair promoter fragment and a nontranslated leader sequence

To investigate the cis-acting sequences involved in regulation of a herpes simplex virus gamma 1 gene, deletion analyses of the glycoprotein B (gB) gene promoter were performed. In transfection assays with gB-chloramphenicol acetyltransferase plasmids, high-level constitutive expression from the gB promoter was found with an 89-bp sequence (-69 to +20). Additional sequences in the 5'-transcribed noncoding leader region (+20 to +136) were required for full stimulation by herpes simplex virus infection. Plasmids with progressive deletions of the gB leader sequence demonstrated that chloramphenicol acetyltransferase expression in infected cells was proportional to the length of the leader region retained. In recombinant viruses containing a gB-gC gene fusion, a similar 83-bp (-60 to +23) region of the gB gene was found to promote accurately initiated gC mRNA from the viral genome with the same kinetics as the wild-type gB gene. Although the kinetics of expression remained the same, RNA abundance was greater with a 298-bp (-260 to +38) promoter than with the 83-bp promoter.

Evidence that the herpes simplex virus immediate early protein ICP27 acts post-transcriptionally during infection to regulate gene expression

The herpes simplex virus (HSV-1) immediate early protein ICP27 is a regulatory protein which is essential for virus replication. The phenotype of temperature-sensitive and deletion mutants in ICP27 includes overexpression of some immediate early and early gene products and greatly reduced levels of late gene products. To determine whether regulation by ICP27 occurs primarily at the transcriptional level, we have studied the expression of two immediate early products (ICP4 and ICP27) and two late gene products (glycoprotein B and glycoprotein C) at the level of transcription initiation, accumulation of steady state mRNA, and protein synthesis in an ICP27 temperature-sensitive mutant tsLG4, compared to wild-type HSV-1. At the nonpermissive temperature in tsLG4-infected cells, the two immediate early gene products ICP4 and ICP27 were overexpressed both at the mRNA and protein level although synthesis of these transcripts as measured by nuclear runoff assays was reduced relative to the wild-type HSV-1 infections. The transcription of late gene products glycoprotein B (gB) and glycoprotein C (gC) was lower in runoff assays from tsLG4 infections suggesting that the reduction in the level of late products occurred at the transcriptional level. However, temperature shift experiments in which tsLG4-infected cells were shifted to the nonpermissive temperature at various times after infection showed that the synthesis of late transcripts was not altered 2 hr after the shift whereas both the accumulation of leaky late and late mRNA and the incorporation of [35S]methionine into newly synthesized gB and gC was reduced by 2 hr after the shift to nonpermissive temperature. Therefore, while the synthesis of new transcripts continued, the accumulation of late mRNAs and their translation into protein was reduced when ICP27 was defective, whereas, the converse was found for immediate early products. That is, the synthesis of new transcripts was reduced yet mRNA and protein accumulated to high levels. These results suggest that ICP27 acts at least in part post-transcriptionally to regulate the expression of immediate early and late gene products.

Differential dependence of herpes simplex virus immediate-early gene expression on de novo-infected cell protein synthesis

The time course of accumulation of herpes simplex virus immediate-early (IE) mRNA and the requirement for infected cell protein synthesis for mRNA transcription and accumulation were compared. Measurements of transcription in nuclear run-on assays, accumulation of cytoplasmic mRNA by Northern (RNA) blot hybridization, and rates of infected cell protein synthesis by pulse-labeling did not indicate differences among the five IE gene, consistent with previous studies. However, as a result of varying the amount of de novo protein synthesis after infection, at least three patterns of maximal expression of the IE genes were revealed. Addition of the protein synthesis inhibitor anisomycin to cells coincident with infection resulted in maximal rates of transcription and accumulation of functional ICP0 mRNA, while 0.5 h of infected cell protein synthesis prior to addition of the drug was required for maximal expression of ICP22/47 and ICP27 mRNAs. Maximal expression of ICP4 mRNA occurred only when 1 h of de novo protein synthesis occurred prior to the addition of the drug. These results are discussed in the context of alternative mechanisms for regulating IE gene expression.

Role of alpha-transinducing factor (VP16) in the induction of alpha genes within the context of viral genomes

In herpes simplex virus 1, the five alpha genes are induced by alpha-transinducing factor (alpha TIF; VP16), a virion protein, acting in concert with Oct-1 and other cellular proteins on a cis-acting site in the promoter domain of alpha genes. Because alpha TIF is an essential virion protein, its function as an inducer can best be evaluated only by mutating the cis-acting site. Earlier we reported on a series of 17 mutations in and around the cis-acting site of a 275-bp alpha 27 promoter fused to a reporter gene and recombined into the viral genome. These recombinant viruses were tested in Vero cells in the presence of cycloheximide, and we demonstrated that mutations in the sequence required for Oct-1 binding abolished transactivation whereas mutations in the alpha TIF-dependent GARAT sequence decreased but did not abolish transactivation. We now report that (i) in limited-passage human embryonic lung cells, alpha gene expression from promoters mutated in the GARAT sequences is often higher and more variable than in Vero cells, (ii) in the absence of cycloheximide, the mutant viruses show less significant impairment of reporter gene expression, (iii) Oct-1 can bind either to the overlapping octamer element or to various TAATGARAT sequences with differing degrees of binding strength and these relative binding levels correlate well with levels of gene expression observed in infected cells, (iv) in the cis-acting site upstream of the alpha 4 gene, no degenerate overlapping Oct-1 sequence exists, and therefore in this instance Oct-1 must be binding directly to the TAATGARAT sequence, (v) extension of the alpha 27 promoter by an additional 1,334 bp results in much higher expression of the reporter gene as a result of additional upstream cis-acting sites, and (vi) obliteration of the most proximal Oct-1 binding element within the 275-bp promoter dramatically reduces gene expression even in the presence of the additional upstream cis-acting sites.

A predictive model for DNA recognition by the herpes simplex virus protein ICP4

The herpes simplex virus (HSV) type 1 immediate early protein ICP4 is an essential regulatory enzyme that binds DNA directly in order to stimulate or repress gene expression. The degree of transaction is related to the locations and affinities of the ICP4 binding sites. A number of binding sites have been identified; some sites showed obvious homology to one another, and these were called consensus ICP4 binding sites. Other binding sites did not appear to be related, and these were termed non-consensus sites. We hypothesized, however, that a single model could describe all ICP4 binding sites, given the appropriate characterizations of sites. We performed statistical analyses on a set of ICP4 binding sites and found that the bases important for defining binding were located within a 13 base region. Missing contact analyses on several high-affinity binding sites revealed the same 13 base region as important for critical protein-DNA contacts. From these data we derived the consensus sequence RTCGTCNNYNYSG, where R is purine, Y is pyrimidine, S is C or G, and N is any base. In addition, we found that a better profile for ICP4 binding sites involves use of a matrix of base proportions from the binding site data; sites are analyzed by calculating the Matrix Mean score. We show that this Matrix Mean model could accurately predict the locations of novel ICP4 binding sites. Finally, we analyzed the entire HSV-1 genome for potential ICP4 binding sites and speculate about what these results suggest for the role of ICP4 in viral gene regulation.

The conserved DNA-binding domains encoded by the herpes simplex virus type 1 ICP4, pseudorabies virus IE180, and varicella-zoster virus ORF62 genes recognize similar sites in the corresponding promoters

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), pseudorabies virus (PRV), varicella-zoster virus (VZV), and equine herpesvirus 1 (EHV-1) are all classified as Alphaherpesvirinae. Each of these five viruses encodes an essential immediate-early (IE) regulatory protein referred to as HSV-1 ICP4, HSV-2 ICP4, PRV IE180, VZV ORF62 protein, and EHV-1 IE1, respectively. These five proteins share extensive homology with each other in domains referred to as regions 2 and 4. The HSV-1 ICP4 region 2 domain contains residues that are required for the DNA-binding capability of ICP4. In this report, we describe the expression of region 2 domains from the ICP4, IE180, and ORF62 genes as fusion proteins in Escherichia coli. DNA-binding assays revealed that each of these region 2 fusion proteins binds to a sequence that overlaps the transcription start site in the promoter for the gene encoding the corresponding protein. Each of the sites with high affinity for one or more of these fusion proteins contains the sequence 5'-ATCGT-3'. This sequence spans the mRNA cap site in the HSV-2 ICP4 gene promoter and is immediately upstream from the transcription start site in the EHV-1 IE1 gene. These results suggest that formation of a specific complex between an IE protein and its own gene promoter may be a common mechanism used by Alphaherpesvirinae to autoregulate transcription of an essential IE gene.

The Vmw175 binding site in the IE-1 promoter has no apparent role in the expression of Vmw110 during herpes simplex virus type 1 infection

The immediate-early (IE) genes of herpes simplex virus type 1 (HSV-1) are the first to be expressed during infection in tissue culture. Since they are transcribed at abnormally high levels in the absence of IE protein synthesis they appear to be subject to repression during normal infection. One of the major HSV-1 regulatory proteins, Vmw175 (the product of IE gene 3), is required for normal IE gene regulation since mutations which inactivate it lead to abnormally high levels of IE gene expression. The mechanism of repression of the IE-3 promoter requires both the ability of Vmw175 to bind to DNA and the presence of a Vmw175 recognition DNA binding sequence at the cap site of the IE-3 promoter. A similar Vmw175 DNA binding sequence has been defined within the IE-1 promoter. This paper describes the construction of a variant of HSV-1 with a mutation within the IE-1 Vmw175 DNA binding site. Although the mutation destroyed the ability of Vmw175 to bind to the site, and greatly reduced the ability of Vmw175 to repress the IE-1 promoter in transfection assays, the mutation had no effect on the levels of Vmw110 expression during normal HSV-1 infection.

Analysis of the herpes simplex virus type 1 promoter controlling the expression of UL38, a true late gene involved in capsid assembly

The cistrons encoding the herpes simplex virus type 1 (HSV-1) UL37 and UL38 genes are adjacent to one another but are transcribed from opposite strands of the viral DNA. The UL37 gene encodes a 1,123-amino-acid protein of unknown function, while the 465-amino-acid UL38 protein is involved in capsid assembly. Previous work from our laboratory indicated that the transcripts encoding these proteins are expressed with significantly different kinetics in productive infection. In the present communication we confirm the kinetic classes and precisely map the cap sites of the UL37 and UL38 mRNAs. A bifunctional reporter gene vector was used to demonstrate that divergent promoters control the expression of these reporter genes in trans-activation assays. The UL38 promoter is functionally separable from that controlling UL37 in a recombinant virus. We used deletion analysis to demonstrate that as few as 29 bases 5' of the mRNA cap site are adequate for full activity of the UL38 promoter in trans-activation assays. Finally, we analyzed the protein-binding properties of the UL38 promoter; several sites that form complexes containing ICP4, with clear homology to those identified in the HSV-1 gamma 42 promoter, are present. Thus, in general, the properties of this promoter are quite similar to those of other gamma promoters.

Regulation of herpes simplex virus immediate-early gene promoters in mouse neuroblastoma cells

The non-permissivity of C1300 mouse neuroblastoma cells for herpes simplex virus (HSV) infection is due to a failure of such cells to transcribe the immediate-early (IE) genes following viral infection. We have transfected both C1300 cells and permissive cells with constructs in which each of the 5 IE promoters drives expression of the readily assayable chloramphenicol acetyl transferase (CAT) gene. These experiments show that the lack of IE gene transcription in C1300 cells is due to the weak activity of the five IE promoters in these cells compared to that observed in a range of permissive cell types. This effect is mediated both by up-stream elements and by sequences present in the minimal promoter. The different effects of DNA concentration on the activities of the minimal and complete promoters suggests that the up-stream sequences act by binding a repressor factor present in C1300 cells whilst the weak activity of the minimal promoter results from the absence of a positive factor in such cells.

Codons 262 to 490 from the herpes simplex virus ICP4 gene are sufficient to encode a sequence-specific DNA binding protein

The HSV-1 immediate early (IE) protein ICP4 (alpha 4, IE175, Vmw175) is an oligomeric molecule which activates transcription of viral early genes, represses transcription of viral IE genes, and binds to specific sequences in certain viral promoters. The extent to which these functions are interrelated has not been fully established. We have expressed truncated portions of the ICP4 gene in E. coli as trpE fusion proteins. DNA-binding studies with these hybrid proteins revealed that ICP4 residues 262 to 490 are sufficient for sequence-specific DNA-binding. DNA-binding was not detected with polypeptides extending from residue 262 to 464 or from residue 306 to 490. Multiple bands of protein-DNA complexes observed in gel mobility shift assays indicate that residues 262 to 490 may also contribute to the oligomerization of ICP4.

Herpes simplex type 1 activation by Epstein-Barr virus nuclear antigen 1

We have investigated the effect of Epstein-Barr virus nuclear antigen 1 (EBNA-1), a nuclear protein encoded by EBV, on herpes simplex virus type 1 (HSV-1) infection either in cells constitutively expressing EBNA-1 or in transient expression assays. Rat-1 cells and rat embryo fibroblasts (REF) immortalized by c-myc or E1A were transfected with a specific EBV DNA fragment coding for EBNA-1. Cloned cell lines which constitutively expressed this antigen were infected with HSV-1. Our results indicate that in EBNA-1-expressing cells, virus growth was higher than in control cells for different virus strains or rodent cell lines. This increase was maximal when cells were infected at low multiplicity, as determined by virus growth, and correlated with the stimulation of viral DNA synthesis. REF + c-myc and Vero cells were cotransfected by an EBNA-1 expression vector driven by Moloney murine leukaemia virus LTR and HSV-1 immediate-early (alpha 0) or early thymidine kinase upstream promoter regulatory regions linked to chloramphenicol acetyltransferase (CAT) coding sequences as effectors. In both cell lines, stimulation of CAT expression by EBNA-1 was observed only with the immediate-early promoter. These results suggest that EBNA-1 can transactivate immediate-early HSV-1 expression.

Mapping the termini and intron of the spliced immediate-early transcript of equine herpesvirus 1

Equine herpesvirus 1 (EHV-1) has been shown to synthesize a 6.0-kilobase (kb) species of immediate-early (IE) mRNA in productively infected cells. This IE gene region maps within the outer portion (map units 0.79 to 0.83 and 0.96 to 1.00) of the two inverted repeat segments of the short genomic region, and elucidation of its DNA sequence has revealed multiple potential open reading frames (ORFs), including a major ORF of 4,461 nucleotides (F. J. Grundy, R. P. Baumann, and D. J. O'Callaghan, Virology 172:223-236, 1989). Analyses of IE polypeptides synthesized in EHV-1-infected cells (in vivo) and in vitro translation of hybrid-selected IE mRNA indicated that multiple species of IE proteins are encoded by this IE mRNA species. To address the nature of the 6.0-kb IE RNA species, Northern (RNA) blot hybridization, S1 nuclease mapping, and primer extension analyses have been employed. These data revealed that no major introns were detected within the body of the IE transcript. However, the IE mRNA was shown to be spliced at the 5' terminus, such that a 372-base intron containing two small ORFs (19 and 51 amino acids) was removed from the leader region of the transcript. This splicing event reduced the leader region from 625 to 253 bases. S1 and primer extension analyses of the 5' terminus of this transcript revealed that the transcription initiation site is located 24 to 26 bases downstream of the consensus TATAAA motif. The 3' transcription termination site was mapped by S1 nuclease analysis to approximately 10 to 20 bases downstream of the polyadenylation signal, AATAAA. The distance from the stop codon of the major ORF to the polyadenylation site is approximately 300 bases. Results from S1 nuclease experiments indicated that splicing does not occur at the 3' terminus. These studies indicated that the EHV-1 6.0-kb IE mRNA is spliced at the 5' terminus and that alternative splicing of this transcript may function in regulating translation of the IE mRNA species.

DNA binding and gene regulation by the herpes simplex virus type 1 protein ICP4 and involvement of the TATA element

We report the results of fine mapping the sequences responsible for negative regulation of immediate-early (IE) gene 3 by its own gene product, ICP4. Affinity-purified ICP4 binds the transcriptional start site of IE gene 3 and protein-protein interactions induce a secondary mobility shift that footprints exactly as the primary complex. Since these DNA-protein complexes contain ICP4, it is likely that the two differ only in stoichiometry of protein. Additional data show that the DNA-binding domain recognized by ICP4 can be embedded as a cassette in foreign DNA and that native ICP4 will recognize and bind the resulting DNA. In two different immediate-early promoters, the ICP4 binding site can be located either 3' or 5' of the TATA box; however, the ICP4 site is rotationally displaced from the transcription factor IID (TFIID) site by a roughly one-half helical turn, suggesting that ICP4 and TFIID are on the opposite helical face when bound at their respective sites. In the IE1 and IE3 promoters, binding of ICP4 causes an alteration in the helical geometry of the minor groove of the TATA region as visualized by copper footprinting. In contrast, TATA hypersensitivity was not detected in the glycoprotein D promoter (an early gene promoter containing the ICP4 site separated from TATA by eight helical turns) or in an artificial IE3 promoter construct in which the TATA-A4 separation was increased from 2.5 to roughly 5 helical turns. Such stereospecific and distance-dependent conformational alterations in the TATA box under the influence of ICP4 binding may be important in the repression of immediate-early genes.

A 165 kd protein of the herpes simplex virion shares a common epitope with the regulatory protein, ICP4

We have investigated the possibility that immediate-early (IE) protein ICP4 could be a part of herpes simplex virus type 1 (HSV-1) virion particle. Immunodetection with a monoclonal antibody against ICP4 reveals that a component of the virion, migrating at 165 kd, shares a common epitope with this immediate-early protein. Immunolocalization studies on purified virions indicate that the antigen can be detected only in virions without membranes, and is located outside the capsid, most probably in the tegument. Ultrastructural localizations on HSV-1 infected BHK cells extracted with a nonionic detergent confirm that the protein immunoreacting with anti-ICP4 is present in virions.

Identification of immediate-early-type cis-response elements in the promoter for the ribonucleotide reductase large subunit from herpes simplex virus type 2

Regulation of the expression of the herpes simplex virus (HSV) type 2 large subunit of ribonucleotide reductase (ICP10) gene was studied directly by immunofluorescence or by chloramphenicol acetyltransferase analysis with hybrid ICP10 promoter constructions. In Vero cells, cotransfection with DNA encoding HSV IE110 or Vmw65 proteins or HCMV IE2 enhanced expression at least 10-fold. In contrast, expression was minimally enhanced by DNA encoding IE175 at low doses and slightly reduced at high doses. IE110-mediated trans-activation was minimal in primary astrocytes and cells from line 293. However, Vmw65 enhanced expression 20-fold in all cell types. cis-Response elements in the ICP10 promoter include a TAATGARAT-like element and other sequences associated with regulation of IE gene expression and potential SP-1, consensus AP-1, and octamer transcription factor 1 binding elements. Factors that bind to the ICP10 promoter were identified in mock and HSV-infected cell extracts. DNA-protein complex formation, presumably involving Vmw65, was demonstrated by gel retardation analysis with mixtures of uninfected cell nuclear extracts and virion lysates. The octamer transcription factor 1 motif (ATGCAAAT) was necessary for optimal Vmw65 binding to the ICP10 promoter as evidenced by competition experiments with oligonucleotides overlapping the consensus IE110 promoter virion response element. The data suggest that ICP10 can be regulated as an immediate-early gene.

ICP4-binding sites in the promoter and coding regions of the herpes simplex virus gD gene contribute to activation of in vitro transcription by ICP4

The herpes simplex virus immediate-early gene product ICP4 activates the transcription of viral early and late genes. We characterized the DNA sequence elements of the early glycoprotein D (gD) gene that play a role in the response to ICP4 in vitro. Using gel mobility shift assays and DNase I footprinting, we identified three ICP4-binding sites, two 5' to the mRNA start site and a third within the coding region. Site II, which gave a footprint between nucleotides -75 and -111 relative to the RNA start site, was previously identified by Faber and Wilcox and contained the reported consensus ICP4-binding site. Site III, which was located between nucleotides +122 and +163, was very similar to the site II sequence, including a core consensus binding sequence, TCGTC. The site I sequence (nucleotides -308 to -282), however, did not share significant homology with either site II or site III. In vitro transcription experiments from mutant constructs of the gD promoter indicated that all three ICP4-binding sites contribute to the stimulation of transcription by ICP4. DNase I footprinting of the gD promoter with uninfected nuclear extracts of HeLa cells showed protection of two very G-rich sequences between nucleotides -33 and -75. We propose that optimal transcription of the gD gene depends on the interaction of ICP4 with multiple binding sites across the gene and cellular factors that recognize specific sequence elements in the promoter.

Stimulation of estrogen receptor mRNA levels in MCF-7 cells by herpes simplex virus infection

Infection of estrogen-responsive cells (MCF-7) with herpes simplex virus type 1 or 2 stimulates expression of the estrogen receptor message. Experiments on infection with the mutant virus, tsK, together with transfection studies implicate the virion protein, Vmw65, in the response. Cellular protein synthesis is essential for estrogen receptor mRNA expression.

Herpes simplex virus type 2 mutants with deletions in the intergenic region between ICP4 and ICP22/47: identification of nonessential cis-acting elements in the context of the viral genome

In herpes simplex virus type 2, the mRNAs of ICP4 and ICP22/47 are divergently transcribed and their transcription initiation sites are separated by 750 base pairs (L. J. Whitton and J. B. Clements, Nucleic Acids Res. 12:2061-2078, 1984). This 750-base-pair region contains many recognized cis-acting elements, including two TATA boxes, numerous Sp1-binding sites, four TAATGARAT motifs, at least one ICP4-binding site, and two origins of replication (oriS) linked in tandem. In this report, we describe the construction of mutant viruses with defined deletions that eliminate these elements either singly or in combination. The phenotypic properties of these mutants indicate that (i) the TAATGARAT motifs and their neighboring elements affect the levels of transcription of both ICP4 and ICP22/47 similarly, (ii) the TATA box serving ICP4 is required for efficient ICP4 mRNA synthesis and for determining the initiation site of transcription, (iii) the ICP4-binding site located at the start of ICP4 transcription is at least partially responsible for the decreased levels of ICP4 mRNA observed in the presence of immediate-early and early gene products, and (iv) mutants bearing deletions that eliminate the entire conventionally recognized ICP4 promoter generate sufficient ICP4 mRNA to maintain viability in cells not expressing ICP4. Additionally, our inability to generate viable deletion mutants lacking all copies of oriS suggests that at least one copy of oriS may be essential for virus replication.

Mutational analysis of the herpes simplex virus trans-inducing factor Vmw65

Vmw65 is a structural component of herpes simplex virus which, in conjunction with host factors, trans-activates the expression of the viral immediate-early genes. In order to examine the relationship between the primary structure of Vmw65 and its trans-activating function, we generated in-frame insertion, deletion, and nonsense mutations in a cloned copy of the gene. The ability of the mutant polypeptides to function as transcriptional activators was assessed by transient transfection of Vero cells using, as the reporter gene, the Escherichia coli chloramphenicol acetyltransferase (cat) gene linked to the promoter-regulatory region from the HSV-1 immediate-early gene coding for Vmw175. These studies have demonstrated that a highly acidic region near the C-terminus of Vmw65 as well as the structural integrity of several other regions of the polypeptide are essential for its transactivating properties, whereas a small region near the N-terminus of the polypeptide is dispensible for activity. Finally, in vivo competition studies using inactive deletion mutants suggest that a domain of the polypeptide located between amino acids 141 and 185 may be involved in protein-protein interactions.

Characterization of the DNA-binding properties of herpes simplex virus regulatory protein ICP4

ICP4 is a herpesvirus-encoded protein that is expressed during the immediate-early phase of productive infection and is required for efficient transcription of viral genes during the early and late phases of infection. Previous studies have shown that ICP4 is a component of specific protein-DNA complexes but have not revealed whether native ICP4 directly recognizes specific nucleotide sequences. Using DNA affinity chromatography, we have purified ICP4 to near homogeneity. The purified preparation consists primarily of dimeric and tetrameric forms of ICP4. As shown by DNase protection experiments, purified ICP4 binds directly to specific sequences in viral DNA. The stability of ICP4-DNA complexes is increased over 100-fold by shifting the temperature from 23 to 4 degrees C. The equilibrium dissociation constant of ICP4-DNA complexes formed at 4 degrees C in the presence of 100 mM NaCl was determined to be approximately 1.1 nM.

Identification of proteins encoded by Epstein-Barr virus trans-activator genes

Specific antisera were generated to characterize Epstein-Barr virus proteins reported to have trans-activating properties. Open reading frame BRLF1 was found to be expressed in two modifications in vivo, with molecular sizes ranging from 94 to 98 kilodaltons (kDa) depending on the cell line, whereas only one protein (Raji cells, 96 kDa) was detected by in vitro translation. Open reading frame BZLF1 encoded polypeptides of 38 and 35 kDa and additional smaller forms. A BZLF1-encoded 30-kDa protein could be detected under conditions in which expression was restricted to immediate early genes. Nuclear localization could be detected under conditions in which expression was restricted to immediate early genes. Nuclear localization could be shown for the proteins derived from reading frames BZLF1 and BMLF1. BMLF1 expression gave a heterogeneous protein pattern, with molecular sizes between 45 and 70 kDa, including a predominant 60-kDa protein detected in different B-cell lines.

The herpes simplex virus type 1 alpha protein ICP27 can act as a trans-repressor or a trans-activator in combination with ICP4 and ICP0

The herpes simplex virus type 1 (HSV-1) alpha proteins ICP4, ICP0, and ICP27 are trans-acting proteins which affect HSV-1 gene expression. To investigate potential interactions between these alpha products and to determine the specificity of action of the alpha proteins in combination with each other compared with their activities individually, we performed a series of transient-expression assays. In these assays we used plasmids containing the alpha genes encoding ICP4, ICP0, and ICP27 either singly or in combination as effectors and HSV-1 genes of different kinetic classes and heterologous genes as targets. The HSV-1 targets consisted of promoter-regulatory domains from alpha (ICP0 and ICP27), beta (thymidine kinase and alkaline exonuclease), beta-gamma (glycoprotein D, glycoprotein B, and VP5), and gamma (glycoprotein C) genes, each fused to the chloramphenicol acetyltransferase (CAT) gene. The heterologous target genes consisted of the simian virus 40 early promoter with enhancer and the Rous sarcoma virus long terminal repeat promoter and enhancer each fused to the CAT gene. Target promoter activity was measured by the assay of CAT activity in extracts of transfected cells and by Northern (RNA) blot hybridization of CAT mRNA. The results of these experiments showed that ICP4 activated only HSV-1 target genes, whereas ICP0 activated all of the targets and ICP27 had little effect on any of the targets. ICP4 and ICP0 had a synergistic effect when inducing HSV-1 targets, but they did not have this effect on the heterologous targets pSV2-CAT or pRSV-CAT. In fact, lower levels of CAT activity and CAT mRNA were found in the presence of both effectors than with ICP0 alone. Most interestingly, although the effector plasmid containing the ICP27 gene had little effect on its own, two different and marked effects depending on the target were observed when ICP27 was combined with ICP4 or ICP0 or both. A trans-repression of the induction seen with ICP4 and ICP0 was found when ICP27 was present in the transfections with pSV2-CAT, pRSV-CAT, pICP0-CAT, pICP27-CAT, pTK-CAT, pgD-CAT, pgB-CAT, and pgC-CAT. This resulted in CAT activity levels which were similar to or lower than the basal level of expression of the target genes in the absence of effector plasmids. This trans-repression occurred over a wide range of concentrations of input ICP27 plasmid. In contrast to this repressive effect of ICP27, a trans-activation was seen when ICP4, ICP0, and ICP27 plasmids were combined in transfections with pAE-CAT and pVP5-CAT as targets. This trans-activation also occurred over a 10-fold range of input ICP27 plasmid. These results suggest that ICP27 can facilitate both down

Role for DNA-protein interaction in activation of the herpes simplex virus glycoprotein D gene

On the basis of experiments with mutant virus and transfection with isolated genes, the herpes simplex virus immediate-early gene product ICP4 is known to positively regulate the transcription of viral early and late genes and negatively regulate expression from its own promoter. Binding of ICP4 to DNA sequences in several viral genes has been reported, yet the significance of ICP4-DNA interaction in transcriptional activation remains unclear. We have studied this problem by using the early glycoprotein D (gD) gene, which possesses a binding site at approximately -100 relative to the RNA initiation site. We linked this promoter and various mutant constructs to the chloramphenicol acetyltransferase gene in order to measure promoter activity in transient transfections both in the presence and in the absence of an ICP4-encoding plasmid. The natural promoter was activated 3.3-fold, and a deletion construct lacking the binding site was activated minimally (1.7-fold). Constructs containing multiple tandem repeats of the binding site (three or five inserts) demonstrated higher expression in the presence of ICP4 than did the natural promoter while retaining low levels of expression when unstimulated. Gel mobility shift assays and DNase I footprinting analyses indicated that ICP4 associated with multiple binding sites. In vitro transcription from a gD promoter construct containing multiple binding sites showed increased RNA synthesis in the presence of partially purified ICP4. These data provide the first direct evidence that binding of ICP4 to a specific DNA sequence in the gD gene contributes to activation of transcription.

Direct correlation between a negative autoregulatory response element at the cap site of the herpes simplex virus type 1 IE175 (alpha 4) promoter and a specific binding site for the IE175 (ICP4) protein

In transient-expression assays, the IE175 (alpha 4) promoter region of herpes simple virus is down-regulated after cotransfection with DNA encoding its own protein product (IE175 or ICP4). The inhibition by IE175 proved to be highly specific for its own promoter region and did not act on either the herpes simplex virus type 1 IE110 (alpha 0) or human cytomegalovirus major immediate-early promoters. Furthermore, the inhibition was still exhibited by IE175 effector plasmids driven by strong heterologous promoters and therefore must be a direct autoregulatory response that cannot be explained by promoter competition effects. In gel mobility retardation assays with infected-cell nuclear extracts, a prominent and specific DNA-protein complex was formed with DNA fragments containing sequences from -108 to +30 in the IE175 promoter region. This activity was not present in mock-infected samples. Even stronger binding occurred with a fragment containing sequences from -128 to +120 in the IE110 promoter, but this second locus was not associated with any detectable response phenotype in cotransfection assays. Supershift experiments with an anti-IE175 monoclonal antibody confirmed the presence of the IE175 protein in both DNA-protein complexes. In the IE175 promoter, specific binding correlated closely with the presence of an intact autoregulatory signal near the cap site as judged by the loss of both activities in a 3'-deleted promoter fragment lacking sequences from -7 to +30. Insertion of a cloned 30-mer synthetic oligonucleotide sequence from positions -8 to +18 in IE175 restored both IE175 binding activity and the down-regulation phenotype. Direct shift-up assays with a similar 30-base-pair (bp) oligonucleotide containing 21 bp from positions -75 to -55 of IE110 (which encompasses a consensus ATCGTC motif) also produced a specific DNA-protein complex containing the IE175 protein. This ATCGTC motif proved to be a necessary component of both the IE110 and IE175 binding sites, but was insufficient on its own for complex formation. Finally, deletion of 2 bp from positions -3 and -4 within the ATCGTC sequence in the IE175 cap site region abolished both binding activity and the IE175-dependent autoregulation phenotype.

A herpesvirus trans-activating protein interacts with transcription factor OTF-1 and other cellular proteins

Immediate early genes of herpes simplex viruses contain one or more copies of the conserved TAAT-GARAT (where R is purine) DNA motif. A virus-encoded regulatory protein (Vmw65) is believed to stimulate transcription via this element, although the protein does not bind directly to DNA. Overlapping the TAATGARAT element in many cases is an octamer sequence (ATGCAAAT) that is involved both in transcription by RNA polymerases II and III and in adenovirus DNA replication. So far at least two proteins (OTF-1 and OTF-2) have been identified that bind to the octamer. We show that both affinity-purified OTF-1 and OTF-2 bind to the TAATGARAT sequence and that Vmw65 induces the formation of an additional complex that involves OTF-1 and that is further retarded in a band-shift gel assay. Complementation experiments involving addition of purified OTF-1 to nuclear extracts that have been depleted of endogenous OTF-1 show that at least one other cellular factor(s) is required for complex formation. This cellular factor may be involved in recognition of the GARAT sequence.

Mutational dissection of the HSV-1 immediate-early protein Vmw175 involved in transcriptional transactivation and repression

Vmw175 is one of five immediate-early (IE) proteins encoded by herpes simplex virus type-1 (HSV-1). It is required for the transcription of later classes of genes and for the accompanying repression of IE expression. Vmw175 has been shown to be a transactivator of transcription and also to autoregulate its own synthesis. We have made a large number of small, in-frame, insertion and deletion mutants of a plasmid-borne copy of the gene encoding Vmw175. Study of the activity of the resultant mutant polypeptides in transient transfection assays has defined the regions of the protein important for the repression of its own promoter, and for the transactivation of an HSV early promoter in synergy with another HSV IE protein, Vmw110. Large stretches of the protein are relatively unimportant for either function, while the regions most sensitive to disruption correlate to sequences conserved between Vmw175 and VZV 140K, the corresponding transactivating protein of Varicella-Zoster virus. The region from amino acids 275 to 490 is particularly important for both repression and transactivation, whereas that from around 840 to 1100 seems to be more important for transactivation than repression. The nuclear localization signal has been mapped to within residues 682-774.

Regulation of human papillomavirus type 11 enhancer and E6 promoter by activating and repressing proteins from the E2 open reading frame: functional and biochemical studies

E2-C, a protein consisting mainly of the carboxy-terminal 45% of the human papillomavirus type 11 (HPV-11) E2 protein, was expressed from the Rous sarcoma virus long terminal repeat in mammalian cells. It competitively repressed the stimulatory action of the full-length E2 protein on the HPV-11 enhancer located in the upstream regulatory region, as assayed by the expression of a reporter gene from the simian virus 40 (SV40) early promoter in transiently transfected monkey CV-1 cells. A mutation in the initiation codon for E2-C protein eliminated repression. In the human cervical carcinoma cell line C-33A, which apparently lacks endogenous HPV DNA, the HPV-11 enhancer-SV40 promoter and the HPV-11 enhancer in its normal association with the E6 promoter had high constitutive activity. In these cells, E2 proteins had little or no stimulatory effect on the transcriptional activity of the HPV-11 enhancer-SV40 promoter. In contrast, the HPV-11 enhancer-E6 promoter was stimulated by the HPV-11 E2 protein but repressed by the bovine papillomavirus type 1 E2 protein, an effect due either to a quantitative difference in E2 expression levels or to a qualitative difference in the trans-activating abilities of the two E2 proteins. In this cell line, the HPV-11 E2-C protein suppressed both the constitutive activity and the HPV-11 E2 trans activation. The E2-C protein was also produced from an expression vector in Escherichia coli. The E2-C protein present in crude E. coli lysates or purified by DNA affinity chromatography associated in vitro with a specific sequence, ACCN6GGT, in filter-binding assays. Moreover, the protein generated DNase I footprints spanning this motif identical to those of bacterially expressed full-length E2 proteins. This DNA sequence motif is necessary and sufficient for E2 binding in vitro and enhancer trans activation in vivo (H. Hirochika, R. Hirochika, T. R. Broker, and L. T. Chow, Genes Dev. 2:54-67, 1988). Mutations in this sequence that abolished interactions with E2 also precluded binding to the E2-C protein. These data strongly suggest that the full-length E2 protein consists of two functional domains: the amino-terminal half for trans activation and the carboxy-terminal half for DNA binding. The mechanism by which E2-C represses E2-dependent enhancer activity most likely involves competition with E2 for binding to a common transcriptional regulatory site.(ABSTRACT TRUNCATED AT 400 WORDS)