A modular system for the assay of transcription regulatory signals: the sequence TAATGARAT is required for herpes simplex virus immediate early gene activation

A Revision of Herpes Simplex Virus Type 1 Transcription: First, Repress; Then, Express

The herpes virus genome bears more than 80 strong transcriptional promoters. Upon entry into the host cell nucleus, these genes are transcribed in an orderly manner, producing five immediate-early (IE) gene products, including ICP0, ICP4, and ICP22, while non-IE genes are mostly silent. The IE gene products are necessary for the transcription of temporal classes following sequentially as early, leaky late, and true late. A recent analysis using precision nuclear run-on followed by deep sequencing (PRO-seq) has revealed an important step preceding all HSV-1 transcription. Specifically, the immediate-early proteins ICP4 and ICP0 enter the cell with the incoming genome to help preclude the nascent antisense, intergenic, and sense transcription of all viral genes. VP16, which is also delivered into the nucleus upon entry, almost immediately reverses this repression on IE genes. The resulting de novo expression of ICP4 and ICP22 further repress antisense, intergenic, and early and late viral gene transcription through different mechanisms before the sequential de-repression of these gene classes later in infection. This early repression, termed transient immediate-early protein-mediated repression (TIEMR), precludes unproductive, antisense, intergenic, and late gene transcription early in infection to ensure the efficient and orderly progression of the viral cascade.

Antiviral Approaches for the Treatment of Herpes Simplex Virus Infections in Newborn Infants

Herpes simplex virus (HSV) infections in newborns are associated with severe disease and death. Trials conducted by the Collaborative Antiviral Study Group have established the standard of care for the treatment of neonatal HSV disease with marked improvements in morbidity and mortality. We review the studies that have contributed to our understanding of the epidemiology and clinical course of neonatal HSV disease and discuss the landmark trials that have resulted in safe and effective treatment together with improved diagnostics. Although significant advances have been made, neonatal HSV disease continues to have an unacceptably high mortality rate with significant sequelae in survivors. Further research is urgently needed for prevention.

Synergistic effects of deleting multiple nonessential elements in nonreplicative HSV-1 BAC genomic vectors play a critical role in their viability

Nonreplicative Herpes simplex virus type-1 (HSV-1) genomic vectors have already entered into clinical trials for neurological gene therapy thanks to their scalable growth in permissive cells. However, the small transgene capacity of this type of HSV-1 vectors currently used in the clinic represents an important limiting factor as a gene delivery system. To develop high-capacity nonreplicative genomic HSV-1 vectors, in this study we have characterized a series of multiply deleted mutants which we have constructed in bacterial artificial chromosomes (BACs), removing up to 24 kb of unstable or dispensable genomic sequences to allow insertion of transgenes up to this size. We show that synergistic effects of deletions of: the HSV-1 replication origins ori_S and ori_L, the HSV-1 internal repeat region, the remaining ICP4 gene copy and the genes encoding for ICP27, U_L56, U_L55, can severely reduce the growth of these HSV-1 vectors. Given that several of these elements have been characterized as 'non-essential' for viral growth in cell culture by single-deletion experiments of wild-type HSV-1, our study highlights the need to re-evaluate their functional contribution in the context of multiply deleted nonreplicative HSV-1 genomic vectors. Our BAC mutants described here can serve as useful starting platforms to accelerate HSV-1 vector development.

HSV-1 as a Model for Emerging Gene Delivery Vehicles

The majority of viral vectors currently used possess modest cargo capability (up to 40 kb) being based on retroviruses, lentiviruses, adenoviruses, and adenoassociated viruses. These vectors have made the most rapid transition from laboratory to clinic because their small genomes have simplified their characterization and modification. However, there is now an increasing need both in research and therapy to complement this repertoire with larger capacity vectors able to deliver multiple transgenes or to encode complex regulatory regions, constructs which can easily span more than 100 kb. Herpes Simplex Virus Type I (HSV-1) is a well-characterized human virus which is able to package about 150 kb of DNA, and several vector systems are currently in development for gene transfer applications, particularly in neurons where other systems have low efficiency. However, to reach the same level of versatility and ease of use as that of smaller genome viral vectors, simple systems for high-titer production must be developed. This paper reviews the major HSV-1 vector systems and analyses the common elements which may be most important to manipulate to achieve this goal.

Overview of gene delivery into cells using HSV-1-based vectors

This overview describes the considerations involved in the preparation and use of a herpes simplex virus type 1 (HSV-1) amplicon as a vector for gene transfer into neurons. Strategies for gene delivery into neurons, either to study the molecular biology of brain function or for gene therapy, must utilize vectors that persist stably in postmitotic cells and that can be targeted both spatially and temporally in the nervous system in vivo. This unit describes the biology of HSV-1 along with a discussion covering development of amplicon and genomic HSV-1 vectors. Advantages and disadvantages of current HSV-1 vectors are presented, and HSV-1 vectors are compared with other vectors for gene transfer into neurons.

Herpes simplex virus 1 ICP22 inhibits the transcription of viral gene promoters by binding to and blocking the recruitment of P-TEFb

ICP22 is a multifunctional herpes simplex virus 1 (HSV-1) immediate early protein that functions as a general repressor of a subset of cellular and viral promoters in transient expression systems. Although the exact mechanism of repression remains unclear, this protein induces a decrease in RNA polymerase II Serine 2 (RNAPII Ser-2) phosphorylation, which is critical for transcription elongation. To characterize the mechanism of transcriptional repression by ICP22, we established an in vivo transient expression reporter system. We found that ICP22 inhibits transcription of the HSV-1 α, β and γ gene promoters. The viral tegument protein VP16, which plays vital roles in initiation of viral gene expression and viral proliferation, can overcome the inhibitory effect of ICP22 on α-gene transcription. Further immunoprecipitation studies indicated that both ICP22 and VP16 bind to positive transcription elongation factor b (P-TEFb) and form a complex with it in vivo. We extended this to show that P-TEFb regulates transcription of the viral α-gene promoters and affects transcriptional regulation of ICP22 and VP16 on the α-genes. Additionally, ChIP assays demonstrated that ICP22 blocks the recruitment of P-TEFb to the viral promoters, while VP16 reverses this blocking effect by recruiting P-TEFb to the viral α-gene promoters through recognition of the TAATGARAT motif. Taken together, our results suggest that ICP22 interacts with and blocks the recruitment of P-TEFb to viral promoter regions, which inhibits transcription of the viral gene promoters. The transactivator VP16 binds to and induces the recruitment of P-TEFb to viral α-gene promoters, which counteracts the transcriptional repression of ICP22 on α-genes by recruiting p-TEFb to the promoter region.

Overview of gene delivery into cells using HSV-1-based vectors

This overview describes the considerations involved in the preparation and use of herpes simplex virus type 1 (HSV-1) as a vector for gene transfer into neurons. Strategies for gene delivery into neurons, either to study the molecular biology of brain function or for gene therapy, must utilize vectors that persist stably in postmitotic cells and that can be targeted both spatially and temporally in the nervous system in vivo. This unit describes the biology of HSV-1 along with a discussion covering development of amplicon and genomic HSV-1 vectors. Advantages and disadvantages of current HSV-1 vectors are presented, and HSV-1 vectors are compared with other vectors for gene transfer into neurons.

Direct interactions of Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 ORF50/Rta protein with the cellular protein octamer-1 and DNA are critical for specifying transactivation of a delayed-early promoter and stimulating viral reactivation

The Kaposi's sarcoma-associated herpesvirus (KSHV) delayed-early K-bZIP promoter contains an ORF50/Rta binding site whose sequence is conserved with the ORF57 promoter. Mutation of the site in the full-length K-bZIP promoter reduced Rta-mediated transactivation by greater than 80%. The K-bZIP element contains an octamer (Oct) binding site that overlaps the Rta site and is well conserved with Oct elements found in the immediate-early promoters of herpes simplex virus type 1(HSV-1). The cellular protein Oct-1, but not Oct-2, binds to the K-bZIP element in a sequence-specific fashion in vitro and in vivo and stimulates Rta binding to the promoter DNA. The coexpression of Oct-1 enhances Rta-mediated transactivation of the wild type but not the mutant K-bZIP promoter, and Oct-1 and Rta proteins bind to each other directly in vitro. Mutations of Rta within an amino acid sequence conserved with HSV-1 virion protein 16 eliminate Rta's interactions with Oct-1 and K-bZIP promoter DNA but not RBP-Jk. The binding of Rta to both Oct-1 and DNA contributes to the transactivation of the K-bZIP promoter and viral reactivation, and Rta mutants deficient for both interactions are completely debilitated. Our data suggest that the Rta/Oct-1 interaction is essential for optimal KSHV reactivation. Transfections of mouse embryo fibroblasts and an endothelial cell line suggest cell-specific differences in the requirement for Oct-1 or RBP-Jk in Rta-mediated transactivation of the K-bZIP promoter. We propose a model in which Rta transactivation of the promoter is specified by the combination of DNA binding and interactions with several cellular DNA binding proteins including Oct-1.

Green fluorescent protein is a quantitative reporter of gene expression in individual eukaryotic cells

Green fluorescent protein (GFP) has gained widespread use as a tool to visualize spatial and temporal patterns of gene expression in vivo. However, it is not generally accepted that GFP can also be used as a quantitative reporter of gene expression. We report that GFP is a reliable reporter of gene expression in individual eukaryotic cells when fluorescence is measured by flow cytometry. Two pieces of evidence support this conclusion: GFP fluorescence increases in direct proportion to the GFP gene copy number delivered to cells by a replication-defective adenovirus vector, Ad.CMV-GFP, and the intensity of GFP fluorescence is directly proportional to GFP mRNA abundance in cells. This conclusion is further supported by the fact that the induction of GFP gene expression from two inducible promoters (i.e., the TRE and ICP0 promoters) is readily detected by flow cytometric measurement of GFP fluorescent intensity. Collectively, the results presented herein indicate that GFP fluorescence is a reliable and quantitative reporter of underlying differences in gene expression.

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 immediate-early gene expression is required for the induction of apoptosis in human epithelial HEp-2 cells

Wild-type herpes simplex virus type 1 (HSV-1) induces apoptosis in human epithelial HEp-2 cells, but infected cell proteins produced later in infection block the process from killing the cells. Thus, HSV-1 infection in the presence of the translational inhibitor cycloheximide (CHX) results in apoptosis. Our specific goal was to gain insight as to the viral feature(s) responsible for triggering apoptosis during HSV-1 infection. We now report the following. (i) No viral protein synthesis or death factor processing was detected after infection with HSV-1(HFEMtsB7) at 39.5 degrees C; this mutant virus does not inject its virion DNA into the nucleus at this nonpermissive temperature. (ii) No death factor processing or apoptotic morphological changes were detected following infection with UV-irradiated, replication-defective viruses possessing transcriptionally active incoming VP16. (iii) Addition of the transcriptional inhibitor actinomycin D prevented death factor processing upon infection with the apoptotic, ICP27-deletion virus HSV-1(vBSDelta27). (iv) Apoptotic morphologies and death factor processing were not observed following infection with HSV-1(d109), a green fluorescent protein-expressing recombinant virus possessing deletions of all five immediate-early (IE) (or alpha) genes. (v) Finally, complete death factor processing was observed upon infection with the VP16 transactivation domain-mutant HSV-1(V422) in the presence of CHX. Based on these findings, we conclude that (vi) the expression of HSV-1 alpha/IE genes is required for the viral induction of apoptosis and (vii) the transactivation activity of VP16 is not necessary for this induction.

Activity of the human papillomavirus type 16 late negative regulatory element is partly due to four weak consensus 5' splice sites that bind a U1 snRNP-like complex

The human papillomavirus (HPV) life cycle is tightly linked to differentiation of the squamous epithelia that it infects. Capsid proteins, and hence mature virions, are produced in the outermost layer of differentiated cells. As late gene transcripts are produced in the lower layers, posttranscriptional mechanisms likely prevent capsid protein production in less differentiated cells. For HPV type 16 (HPV-16), a 79-nucleotide (nt) negative regulatory element (NRE) inhibits gene expression in basal epithelial cells. To identify key NRE sequences, we carried out transient transfection in basal epithelial cells with reporter constructs containing the HPV-16 late 3' untranslated region with deletions and mutations of the NRE. Reporter gene expression was increased over 40-fold by deletion of the entire element, 10-fold by deletion of the 5' portion of the NRE that contains four weak consensus 5' splice sites, and only 3-fold by deletion of the 3' GU-rich region. Both portions of the element appear to be necessary for full repression. Inactivating mutations in the 5' splice sites in the 5' NRE partially alleviated repression in the context of the 79-nt NRE but caused full derepression when assayed in a construct with the 3' NRE deleted. All four contribute to the inhibitory effect, though the second splice site is most inhibitory. Sm proteins, U1A and U1 snRNA, but not U1 70K, could be affinity purified with the wild-type NRE but not with the NRE containing mutations in the 5' splice sites, indicating that a U1 snRNP-like complex forms upon the element.

The human papillomavirus type 31 late 3' untranslated region contains a complex bipartite negative regulatory element

The papillomavirus life cycle is tightly linked to epithelial cell differentiation. Production of virus capsid proteins is restricted to the most terminally differentiated keratinocytes in the upper layers of the epithelium. However, mRNAs encoding the capsid proteins can be detected in less-differentiated cells, suggesting that late gene expression is controlled posttranscriptionally. Short sequence elements (less than 80 nucleotides in length) that inhibit gene expression in undifferentiated epithelial cells have been identified in the late 3' untranslated regions (UTRs) of several papillomaviruses, including the high-risk mucosal type human papillomavirus type 16 (HPV-16). Here we show that closely related high-risk mucosal type HPV-31 also contains elements that can act to repress gene expression in undifferentiated epithelial cells. However, the HPV-31 negative regulatory element is surprisingly complex, comprising a major inhibitory element of approximately 130 nucleotides upstream of the late polyadenylation site and a minor element of approximately 110 nucleotides mapping downstream. The first 60 nucleotides of the major element have 68% identity to the negative regulatory element of HPV-16, and these elements bind the same cellular proteins, CstF-64, U2AF(65), and HuR. The minor inhibitory element binds some cellular proteins in common with the major inhibitory element, though it also binds certain proteins that do not bind the upstream element.

Heat shock and developmental expression of hsp83 in the filarial nematode Brugia pahangi

hsp83 was cloned from the filarial nematode Brugia pahangi. The mRNA was constitutively expressed at 37 degrees C in life cycle stages that live in the mammalian host (microfilariae and adult worms). Heat shock resulted in only a minimal increase in levels of transcription. A genomic copy of hsp83 was isolated and was shown to contain 11 introns while sequencing of the 5' upstream region revealed several heat shock elements. Using a chloramphenicol acetyltransferase (CAT) reporter gene construct the expression of hsp83 from B. pahangi (Bp-hsp83) was studied by transfection of COS-7 cells. Similar to the expression pattern in the parasite, CAT activity was detected at 37 degrees C and was not influenced by heat shock. When the free-living nematode Caenorhabditis elegans was transfected with the same construct, CAT activity was not observed at normal growth temperatures (21 degrees C) or under moderate heat shock conditions (28 degrees C). However exposure to more severe heat shock (35 degrees C) resulted in an increase in CAT activity. These results suggest that Bp-hsp83 has a temperature threshold > or = 35 degrees C for expression.

HSV-1-based vectors for gene therapy of neurological diseases and brain tumors: part I. HSV-1 structure, replication and pathogenesis

The design of effective gene therapy strategies for brain tumors and other neurological disorders relies on the understanding of genetic and pathophysiological alterations associated with the disease, on the biological characteristics of the target tissue, and on the development of safe vectors and expression systems to achieve efficient, targeted and regulated, therapeutic gene expression. The herpes simplex virus type 1 (HSV-1) virion is one of the most efficient of all current gene transfer vehicles with regard to nuclear gene delivery in central nervous system-derived cells including brain tumors. HSV-1-related research over the past decades has provided excellent insight into the structure and function of this virus, which, in turn, facilitated the design of innovative vector systems. Here, we review aspects of HSV-1 structure, replication and pathogenesis, which are relevant for the engineering of HSV-1-based vectors.

The transcriptional activation domain of VP16 is required for efficient infection and establishment of latency by HSV-1 in the murine peripheral and central nervous systems

The herpes simplex virus (HSV) transactivator VP16 is a structural component of the virion that activates immediate-early viral gene expression. The HSV-1 mutant in1814, which contains a 12-bp insertion that compromises the transcriptional function of VP16, replicated to a low level if at all in the trigeminal ganglia of mice (I. Steiner, J. G. Spivack, S. L. Deshmane, C. I. Ace, C. M. Preston, and N. W. Fraser (1990). J. Virol. 64, 1630-1638; Valyi-Nagy et al., unpublished data). However, in1814 did establish a latent infection in the ganglia after corneal inoculation from which it could be reactivated. In this study, several HSV-1 strains were constructed with deletions in the VP16 transcriptional activation domain. These viruses were viable in cell culture, although some were significantly reduced in their ability to initiate infection. A deletion mutant completely lacking the activation domain of VP16 (RP5) was unable to replicate to any detectable level or to efficiently establish latent infections in the peripheral and central nervous systems of immunocompetent mice. However, similar to in1814, RP5 formed a slowly progressing persistent infection in immunocompromised nude mice. Thus RP5 is severely neuroattenuated in the murine model of HSV infection. However, the activation domain of VP16 is not essential for replication in the nervous system, since we observed a slow progressive infection persisting in the absence of an immune response.

HSV molecular biology: general aspects of herpes simplex virus molecular biology

Comparison of the herpes simplex virus type 1 (HSV-1) DNA sequence with that of other alpha, beta and gamma-herpesviruses, allied with molecular genetic studies have greatly increased understanding of the HSV genome and the functions encoded by individual virus genes and has facilitated the development of rational antiviral strategies. Here we review the coding content of the HSV-1 genome and identify: genes encoding structural components of the capsid, tegument or envelope; genes whose products are essential for growth in tissue culture; and genes that are conserved between members of the alpha, beta and gamma-herpesvirinae. The HSV lifecycle and the main regulation cascade is discussed and genes that present targets for antiviral intervention identified. The protein content of the infectious virion particle is reviewed and compared with that of two additional non-infectious HSV-related particles species (L-particles and pre-DNA replication particles (PREPs)). The potential of HSV-1 L particles and PREP particles as DNA-free HSV-1 vaccine candidates and the desirability of deleting specific gene products from live HSV vaccines is discussed.

The effect of herpes simplex virus type 1 L-particles on virus entry, replication, and the infectivity of naked herpesvirus DNA

Herpes simplex virus type 1(HSV-1) L-particles are known to be composed mainly of envelope and tegument proteins, to lack the nucleocapsid, and to be noninfectious. Thus L-particles represent interesting vaccine candidates. L-particles at > 1000/cell interfered with HSV-1 virion adsorption and penetration While L-particles did not affect HSV-1 growth kinetics in resting or nonresting BHK cultures infected with purified virions, treatment with L-particles before, or after, transfection with HSV-1 DNA resulted in a progressive increase in plaque numbers (five- to sixfold at 1000 L-particles/cell). Transfection assays using HSV-1 ts mutant DNA (ts 1201) revealed that enhancement was due to induction of otherwise nonreplicating genomes. The enhancement obtained with L-particles produced by WT HSV-1 or by mutants that are either deleted, or defective, in certain gene products was compared. Most important were the Vmw110 (ICP0) and Vmw65 (alpha-TIF) proteins, but VP11/12, VP13/14, and vhs also have a role. The L-particle-associated Vmw175 (ICP 4) protein did not appear be involved. The effect of homologous and heterologous combinations of pseudorabies virus, equineherpesvirus-1, and HSV-1 DNA's and L-particles was investigated in transfection assays. The L-particles of each virus, to varying extent, enhanced the plaquing efficiency of their own DNA but were also effective in heterologous combinations.

An improved plasmid DNA expression vector for direct injection into skeletal muscle

In previous work, the direct injection of 50 micrograms of a plasmid DNA vector encoding firefly luciferase (VR1205) into murine quadriceps muscle produced an average of 6.5 ng of luciferase per muscle at 7 days postinjection. In this report, various elements of the VR1205 vector were modified to increase gene expression levels or to eliminate undesired viral sequences. Expression of the modified vectors was then compared to VR1205 using the intramuscular injection assay. In general, modifications to promoter, enhancer, and intronic sequences either decreased luciferase expression levels or had no effect. However, modifications to the polyadenylation and transcriptional termination sequences, plasmid backbone elements, and the luciferase gene itself each increased luciferase expression levels. The best-expressing vector, designated VR1255, contained a combination of these incrementally beneficial changes. A single intramuscular injection of 50 micrograms of VR1255 produced 300 ng of luciferase at 7 days postinjection, an expression level 46-fold higher than the VR1205 vector (or 22-fold higher, excluding modifications to the luciferase gene) and 154-fold higher than a commercially available luciferase expression vector. Thus, VR1255 represents an improved plasmid DNA vector that may be useful for gene therapy applications.

Identification of multiple promoters within the N-ras proto-oncogene

N-ras possesses a 'housekeeping' promoter, being G + C-rich and devoid of a TATA-box. Transcription initiates at a number of locations within this gene, a phenomena that is generally attributed to the absence of a TATA-box. In this report we investigate the possibility that multiple promoters, which could potentially contribute to the observed 5' end heterogeneity, exist within the murine N-ras gene. The 5' region of the gene was subdivided into several fragments, each corresponding to a region in which one or more transcription initiation site(s) had been mapped, and the ability of each fragment to express a reporter gene was assessed. Promoter activity was found associated with three independent, non-overlapping fragments, two of which were located entirely within transcribed regions of the gene. We found that these intragenic promoters were able to express the N-ras gene itself, as well as the reporter gene. In addition, we found that the activity of an intragenic promoter fragment was dependent upon the presence of regions encompassing initiation sites, and that a small fragment (approximately 40 bp) encompassing several initiation sites possessed promoter activity. These data support the existence of an 'initiator' element within the N-ras gene. Overall, our results demonstrate that multiple promoters reside within N-ras and suggest that they may play a role in generating the observed mRNA 5' end heterogeneity. The identification of multiple promoters within N-ras may have important implications regarding the regulation of expression of this gene in normal and malignant tissues. In addition, since a number of other genes with housekeeping promoters also initiate transcription at multiple locations, it is possible that the utilization of multiple promoters may represent a common feature of this class of genes.

The herpes simplex virus type 1 particle: structure and molecular functions. Review article

This review is a summary of our present knowledge with respect to the structure of the virion of herpes simplex virus type 1. The virion consists of a capsid into which the DNA is packaged, a tegument and an external envelope. The protein compositions of the structures outside the genome are described as well as the functions of individual proteins. Seven capsid proteins are identified, and two of them are mainly present in precursors of mature DNA-containing capsids. The protein components of the 150 hexamers and 12 pentamers in the icosahedral capsid are known. These capsomers all have a central channel and are connected by Y-shaped triplexes. In contrast to the capsid, the tegument has a less defined structure in which 11 proteins have been identified so far. Most of them are phosphorylated. Eleven virus-encoded glycoproteins are present in the envelope, and there may be a few more membrane proteins not yet identified. Functions of these glycoproteins include attachment to and penetration of the cellular membrane. The structural proteins, their functions, coding genes and localizations are listed in table form.

Herpes simplex virus VP16 forms a complex with the virion host shutoff protein vhs

Herpes simplex virus (HSV) virions contain at least two regulatory proteins that modulate gene expression in infected cells: the transcriptional activator VP16 and the virion host shutoff protein vhs. VP16 stimulates transcription of the HSV immediate-early genes, and vhs suppresses host protein synthesis and induces accelerated turnover of cellular and viral mRNAs. We report here that vhs binds directly to VP16: vhs and VP16 were coprecipitated from infected cells by an anti-vhs antiserum, and vhs and VP16 protein A fusions each bound intact versions of the other protein in a solid-phase capture assay. In addition, vhs and VP16 interacted in the two-hybrid activator system when coexpressed in Saccharomyces cerevisiae. vhs residues 238 to 344 were sufficient for the interaction, and the VP16 acidic transcriptional activation domain was not required. vhs blocked the ability of VP16 to enter a multiprotein complex on an immediate-early TAATGARATTC consensus sequence, indicating that vhs interacts with one or more regions of VP16 required for promoter recognition. We suggest that this interaction may play a structural role in the assembly of HSV virions and modulate the activity of vhs during infection.

Gene transfer in regenerating muscle

We have compared the efficiency of direct gene transfer in normal and regenerating rat skeletal muscle. Muscle necrosis and regeneration was induced by intramuscular injection of bupivacaine in the soleus muscle of adult rats. Plasmids containing beta-galactosidase (beta-gal) or chloramphenicol acetyltransferase (CAT) genes driven by viral promoters were injected 3 days after bupivacaine treatment into the regenerating and the contralateral uninjured muscles. Expression of CAT activity was > 80-fold higher in regenerating compared to control muscles at 7 days post-transfection, but decreased at 30 and 60 days. Southern blot analysis showed that the predominant form of CAT DNA was episomal in transfected muscles; however, CAT activity measurements performed on the same transfected muscles showed no precise correlation between enzymatic activity and amount of plasmid DNA. Expression of beta-gal was detected in numerous regenerating fibers of the injured soleus muscles at 7 days post-transfection; in contrast, only rare positive fibers were found in control muscles. Focal infiltrates of mononuclear cells, which surround and invade selectively beta-gal-positive fiber segments, were observed at 30 days post-transfection, suggesting that immune mechanisms are implicated in the progressive loss of transgenes with time. The finding that regenerating muscle fibers display a higher efficiency of transfection may be relevant to gene therapy of Duchenne muscular dystrophy, because regenerating fibers are numerous in the early stages of the disease.

Transcriptional up-regulation of the mouse cytosolic glutathione peroxidase gene in erythroid cells is due to a tissue-specific 3' enhancer containing functionally important CACC/GT motifs and binding sites for GATA and Ets transcription factors

Nuclear run-on experiments have shown that the high level of expression of the mouse cytosolic glutathione peroxidase mRNA in erythroid cells is due to up-regulation of the gene at the transcriptional level. Studies of the chromatin structure around the cytosolic glutathione peroxidase gene have revealed a series of DNase I hypersensitive sites (DHSS) in the 3' flanking region of the gene in erythroid and other high-expression tissues that are lacking in low-expression cells, in addition to a DHSS over the promoter region in both high- and low-expression tissues. Functional transfection experiments have demonstrated that one of the 3' DHSS regions functions as an enhancer in erythroid cells but not in a low-expression epithelial cell line; and site-directed mutagenesis and footprinting experiments reveal that the activity of the erythroid cell-specific enhancer requires a cluster of binding sites for the CACC/GT box factors and the GATA and Ets families of transcription factors.

Transcriptional up-regulation of the mouse cytosolic glutathione peroxidase gene in erythroid cells is due to a tissue-specific 3' enhancer containing functionally important CACC/GT motifs and binding sites for GATA and Ets transcription factors

Nuclear run-on experiments have shown that the high level of expression of the mouse cytosolic glutathione peroxidase mRNA in erythroid cells is due to up-regulation of the gene at the transcriptional level. Studies of the chromatin structure around the cytosolic glutathione peroxidase gene have revealed a series of DNase I hypersensitive sites (DHSS) in the 3' flanking region of the gene in erythroid and other high-expression tissues that are lacking in low-expression cells, in addition to a DHSS over the promoter region in both high- and low-expression tissues. Functional transfection experiments have demonstrated that one of the 3' DHSS regions functions as an enhancer in erythroid cells but not in a low-expression epithelial cell line; and site-directed mutagenesis and footprinting experiments reveal that the activity of the erythroid cell-specific enhancer requires a cluster of binding sites for the CACC/GT box factors and the GATA and Ets families of transcription factors.

Identification of a promoter mapping within the reiterated sequences that flank the herpes simplex virus type 1 UL region

Analysis of the promoter for the herpes simplex virus (HSV) immediate-early (alpha) gene alpha 0 in a short-term transient expression assay revealed that a SacI-to-NcoI fragment from -786 to +148 relative to the cap site directed the synthesis of chloramphenicol acetyltransferase when the fragment was present in either orientation. Although the constitutive levels of promoter activity were similar with either orientation, the reverse-orientation promoter was not induced in response to infection with HSV. Analysis of sequences composing the putative promoter in the opposite orientation revealed the presence of important regulatory elements associated with alpha promoters. These include an alpha-trans-inducing factor (alpha-TIF)-like response element, a high-affinity ICP4-binding site, numerous Sp1-binding sites, and a TATA box. Sequences contained within this region formed specific DNA-protein complexes in extracts from mock-infected and HSV-infected HeLa cells. Transient expression assays revealed that this sequence was positively regulated by the alpha 0 and alpha-TIF genes but negatively regulated by alpha 4. Finally, nuclear run-on transcription assays revealed that this promoter is active in its correct genomic context during the course of virus infection. We suggest that the promoter is a hybrid between an alpha and beta promoter because it exhibits maximal expression at 8 h postinfection and is expressed in the presence of cycloheximide.

Herpes simplex virus IE63 acts at the posttranscriptional level to stimulate viral mRNA 3' processing

We have shown previously that a novel herpes simplex virus-induced activity, LPF, selectively increases RNA 3'-end processing at the poly(A) site of a late virus gene (J. McLauchlan, S. Simpson, and J. B. Clements, Cell 59:1093-1105, 1989). Here, our in vivo and in vitro analyses both demonstrate that LPF is induced during early stages of virus infection. Studies of virus mutants indicate that expression of the immediate-early IE63 gene is required for induction of this activity. The selective effects on 3' processing displayed in the presence of IE63 provide direct evidence that IE63 can influence this posttranscription process. This extends previous studies which reported increases in reporter gene activity with certain poly(A) sites by IE63 (R. M. Sandri-Goldin and G. E. Mendoza, Genes Dev. 6:848-863, 1992).

Recognition of the surface of a homeo domain protein

Homeo domain proteins exhibit distinct biological functions with specificities that cannot be predicted by their sequence specificities for binding DNA. Recognition of the surface of the Oct-1 POU homeo domain provides a general model for the contribution of selective protein-protein interactions to the functional specificity of the homeo domain family of factors. The assembly of Oct-1 into a multiprotein complex on the herpes simplex virus alpha/IE enhancer is specified by the interactions of its homeo domain with ancillary factors. This complex (C1 complex) is composed of the viral alpha TIF protein (VP16), Oct-1, and one additional cellular component, the C1 factor. Variants of the Oct-1 POU homeo domain were generated by site-directed mutagenesis, which altered the residues predicted to form the exposed surface of the domain-DNA complex. Proteins with single amino acid substitutions on the surface of either helix 1 or 2 of the Oct-1 POU homeo domain had decreased abilities to form the C1 complex. The behavior of these mutants in a cooperative DNA-binding assay with alpha TIF suggested that the Oct-1 POU homeo domain is principally recognized by alpha TIF in the C1 complex. The preferential recognition of Oct-1 over the closely related Oct-2 protein is critically influenced by a single residue on the surface of helix 1 because the introduction of this residue into the Oct-2 POU homeo domain significantly enhanced its ability to form a C1 complex.

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.

The serum response element and an AP-1/ATF sequence immediately downstream co-operate in the regulation of c-fos transcription

Transcription of the c-fos gene is activated in response to a wide variety of extracellular stimuli and several cis-acting transcriptional control elements have been characterized. One of these elements is called the serum response element (SRE) and here we investigate an interaction between this element and an AP-1/ATF-like sequence immediately downstream from the SRE. In growing cells these sequences activate transcription in an additive fashion whereas in quiescent cells they co-operate to repress transcription. This co-operation is disrupted upon separation of the elements which also alters the response of the elements to serum or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) stimulation of quiescent cells. This separation also results in an increase of transcription in growing cells. A consensus AP-1 DNA-binding site can substitute for the AP-1/ATF-like sequence present in the c-fos promoter to activate transcription in an additive fashion with the SRE in growing cells, and co-operate in repression in quiescent cells. These observations show that any interaction that may be occurring between proteins binding to these elements results in a different pattern of transcriptional control in growing and quiescent cells. Alternatively, different proteins (or modified proteins) may complex with these sequences in the two different states of cell growth.

The UL5 gene of herpes simplex virus type 1: isolation of a lacZ insertion mutant and association of the UL5 gene product with other members of the helicase-primase complex

The UL5 gene product is required continuously during viral DNA synthesis (L. Zhu and S. K. Weller, Virology 166:366-378, 1988) and has been shown to be a component of a three protein helicase-primase complex encoded by herpes simplex virus type 1 (J. J. Crute, T. Tsurumi, L. Zhu, S. K. Weller, P.D. Olivo, M. D. Challberg, E. S. Mocarski, and I. R. Lehman, Proc. Natl. Acad. Sci. USA 86:2186-2189, 1989). The other members of the complex are viral proteins encoded by genes UL8 and UL52. In this study, we isolated a permissive cell line (L2-5) which contains the wild-type UL5 gene under the control of the strong and inducible promoter for the large subunit of herpes simplex virus type 1 ribonucleotide reductase (ICP6). An insertion mutant containing a mutation in the UL5 gene (hr99) was isolated by using the insertional mutagen ICP6::lacZ, in which the Escherichia coli lacZ gene is expressed under control of the viral ICP6 promoter. When grown on Vero cells, hr99 does not form plaques or synthesize viral DNA, although both defects are complemented efficiently on the L2-5 cells. These results confirm that the UL5 gene product is essential for viral growth and DNA replication. Furthermore, since no detectable UL5 protein is synthesized in hr99-infected cells, these cells provide a valuable control not only for the detection of the UL5 protein itself but also for the detection of protein-protein interactions with UL8 and UL52 by coimmunoprecipitation. In addition, the lacZ insertion in hr99 provides a convenient screening system for the introduction of site-specific mutations into the viral genome (L. Zhu and S. K. Weller, J. Virol. 66:469-479, 1992). Thus, hr99 is a valuable tool in the structure-function analysis of the UL5 gene.

trans activation of the simian virus 40 late promoter by large T antigen requires binding sites for the cellular transcription factor TEF-1

Simian virus 40 (SV40) T antigen stimulates the level of transcription from several RNA polymerase II promoters, including the SV40 late promoter. The mechanism of trans activation appears to be indirect since binding of T antigen to specific DNA sequences is not required. However, specific promoter elements that respond to T antigen have not previously been defined. We identified DNA sequences from the SV40 late promoter whose ability to stimulate transcription is induced by the expression of T antigen. In particular, the Sph I + II motifs of the SV40 enhancer can confer T-antigen inducibility to the normally uninducible herpes simplex virus thymidine kinase gene promoter when multiple copies of the sequence are inserted 5' of the transcription initiation site and TATA sequence. Binding sites for the cellular transcription factor TEF-1 and octamer binding proteins are contained within the Sph I + II motifs, as well as at other positions in the SV40 promoter. To study the role of individual protein-binding sites in trans activation by T antigen, mutations were constructed in various TEF-1 and octamer protein-binding sites of the SV40 late promoter. These mutations did not significantly affect basal promoter activity. However, mutation of all three TEF-1 sites prevented detectable activation by T antigen. DNase I footprinting of the mutated promoters with purified proteins demonstrated that inducibility by T antigen correlated with binding affinity of TEF-1 for the DNA and not with binding affinity of an octamer binding protein.

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.

Regulation of herpes simplex virus true late gene expression: sequences downstream from the US11 TATA box inhibit expression from an unreplicated template

The true late genes of herpes simplex virus type 1 (HSV-1) are expressed only after the onset of viral DNA replication. Previous studies demonstrated that late promoters lack elements upstream of the TATA box and suggested that only a subset of TATA elements can function in the context of true late promoters. We determined which structural features of true late promoters are responsible for the stringent requirement for viral DNA replication by inserting a series of simple model constructs into the HSV-1 genome in place of one of the two promoters of the UL24 gene. An oligonucleotide consisting of 19 nucleotides spanning the TATA box of the HSV-1 true late US11 gene drove barely detectable levels of expression; by contrast, the corresponding regions of the Adenovirus type 2 major late promoter and the HSV-1 true late glycoprotein C promoter were much more active. Transcripts driven from all of these minimal TATA box promoters accumulated without viral DNA replication. The activity of the US11 TATA box was stimulated by adding upstream Sp1-binding sites or placing the US11 or rabbit beta-globin cap/leader region (-11 to +39) downstream. The Sp1-TATA and TATA-beta-globin cap/leader constructs remained replication independent, while the TATA-US11 cap/leader promoter displayed true late regulation. These results demonstrate that sequences located within the US11 cap/leader region impose a strict requirement for viral DNA replication on a minimal TATA box promoter.

Identification of Ets- and notch-related subunits in GA binding protein

Recombinant cDNA clones that encode two distinct subunits of the transcription factor GA binding protein (GABP) have been isolated. The predicted amino acid sequence of one subunit, GABP alpha, exhibits similarity to the sequence of the product of the ets-1 protooncogene in a region known to encompass the Ets DNA binding domain. The sequence of the second subunit, GABP beta, contains four 33-amino acid repeats located close to the NH2-terminus of the subunit. The sequences of these repeats are similar to repeats in several transmembrane proteins, including Notch from Drosophila melanogaster and Glp-1 and Lin-12 from Caenorhabditis elegans. Avid, sequence-specific binding to DNA required the presence of both polypeptides, revealing a conceptual convergence of nuclear transforming proteins and membrane-anchored proteins implicated in developmentally regulated signal transduction processes.

Identification of two protein binding sites within the varicella-zoster virus major immediate early gene promoter

Binding sites for cellular proteins in the promoter of the varicella-zoster virus (VZV) major immediate early (IE) gene were investigated. Protein binding was detected at sequence motifs possessing homology to the CCAAT element and an ATF/AP-1-like binding site, and recognition of the ATF/AP-1 site was apparently facilitated by occupation of the CCAAT site. Gene expression directed by the VZV major IE promoter was stimulated by the adenovirus 5, 289 amino acid EIA gene product. The implications of the results for VZV gene expression and replication are discussed.

A negative regulatory element in the human papillomavirus type 16 genome acts at the level of late mRNA stability

A negative regulatory element present in the human papillomavirus type 16 genome has been characterized. Deletion analysis has localized the 5' end of the element to the late region of the genome at the extreme 3' end of the coding region of the L1 open reading frame, around the L1 stop codon, with the element extending into the L1 3' untranslated region. For the cell lines used, the element's function was independent of cell type, tissue, or species of origin, unlike papillomavirus infection, which is very dependent on such factors. By using an mRNA decay assay, we have determined that polyadenylated RNA containing the element is much less stable than polyadenylated RNA lacking the element. This indicates that the element acts as an mRNA instability element. The significance of A-rich, GU-rich, and AUG-rich sequences for the functioning of this human papillomavirus type 16 instability element is discussed.

Electroporation of lymphoid cells: factors affecting the efficiency of transfection

We have increased the efficiency of electroporation of lymphoid cells over fifty fold by optimising several biological and electrical parameters. Under optimised conditions, the electroporation efficiency was comparable to that reported for other cell types. Actively dividing cells were crucial for high transient transfection signal. The two most important electrical parameters were high capacitance (960 microF) and moderate decay constants in the range of 10-15 ms. The optimal field strength depended on the cell line, but was in the range 0.6-1 kV/cm. Administering the pulse in medium lacking serum gave higher efficiency than when isotonic salt solution was used and the transfection signal was depressed if cells and DNA were allowed to incubate for several minutes either before or after the pulse. Electroporation was carried out at room temperature and there was no advantage in using low temperatures (0-4 degrees C). When electroporated cells were grown in conditioned medium, the signal was enhanced about two fold depending on the source of the conditioned medium.

Interaction of epsilon-globin cis-acting control elements with erythroid-specific regulatory macromolecules

We have used a competition assay to investigate the influence of erythroid-specific cellular factors on transcription from the human epsilon-globin major cap site promoter and the minor promoter located 200 base pairs (bp) upstream from the epsilon-globin cap site. In the human erythroid cell line K562, competition of the epsilon-globin major cap site promoter linked to the chloramphenicol acetyltransferase (CAT) gene (epsilon P-CAT) with the same promoter fragment linked to a neomycin resistance gene (epsilon P-NEO) leads to a reduction in CAT activity. This indicates the specific presence of K562 cells of factor(s) which interact with the 200-bp promoter fragment (isolated from the gene body or flanking sequences) to activate transcription from the epsilon-globin major cap site. Competition of the epsilon-globin major promoter (as epsilon P-CAT) with the upstream minor epsilon-globin promoter (as epsilon P2-NEO) also leads to a reduction in CAT activity, indicating that both promoters share erythroid-specific trans-acting factors. The reverse competition (epsilon P2-CAT with epsilon P-NEO) leads to an increase in CAT activity, suggesting that the existence of erythroid-specific factor(s) which repress transcription from the 200-bp-upstream epsilon-globin promoter.

A short, highly repetitive element in intron -1 of the human c-Ha-ras gene acts as a block to transcriptional readthrough by a viral promoter

We have identified a short, highly repetitive element within intron -1 of the human c-Ha-ras gene. This element was found to be transcribed in both orientations and to be homologous to heterogeneous nonpolyadenylated transcripts. The repetitive element blocked transcriptional readthrough from a strong upstream viral promoter but allowed unimpaired readthrough from the c-Has-ras promoter. We suggest that it may serve to prevent excessive transcription into the coding region of the gene under such circumstances as viral insertion.

A short, highly repetitive element in intron -1 of the human c-Ha-ras gene acts as a block to transcriptional readthrough by a viral promoter

We have identified a short, highly repetitive element within intron -1 of the human c-Ha-ras gene. This element was found to be transcribed in both orientations and to be homologous to heterogeneous nonpolyadenylated transcripts. The repetitive element blocked transcriptional readthrough from a strong upstream viral promoter but allowed unimpaired readthrough from the c-Has-ras promoter. We suggest that it may serve to prevent excessive transcription into the coding region of the gene under such circumstances as viral insertion.

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.

Procyclic acidic repetitive protein (PARP) genes located in an unusually small alpha-amanitin-resistant transcription unit: PARP promoter activity assayed by transient DNA transfection of Trypanosoma brucei

At least one of the procyclic acidic repetitive protein (PARP or procyclin) loci of Trypanosoma brucei is a small (5- to 6-kilobase) polycistronic transcription unit which is transcribed in an alpha-amanitin-resistant manner. Its single promoter, as mapped by run-on transcription analysis and UV inactivation of transcription, is located immediately upstream of the first alpha-PARP gene. Transcription termination occurs in a region approximately 3 kilobases downstream of the beta-PARP gene. The location of the promoter was confirmed by its ability to direct transcription of the bacterial chloramphenicol acetyltransferase gene in insect-form (procyclic) T. brucei. The putative PARP promoter is located in the region between the 3' splice acceptor site (nucleotide position 0) and nucleotide position -196 upstream of the alpha-PARP genes. Regulatory regions influencing the levels of PARP expression may be located further upstream. We conclude that a single promoter, which is located very close to the 3' splice acceptor site of the alpha-PARP genes, directs the transcription of a small, polycistronic, and alpha-amanitin-resistant transcription unit.

Procyclic acidic repetitive protein (PARP) genes located in an unusually small alpha-amanitin-resistant transcription unit: PARP promoter activity assayed by transient DNA transfection of Trypanosoma brucei

At least one of the procyclic acidic repetitive protein (PARP or procyclin) loci of Trypanosoma brucei is a small (5- to 6-kilobase) polycistronic transcription unit which is transcribed in an alpha-amanitin-resistant manner. Its single promoter, as mapped by run-on transcription analysis and UV inactivation of transcription, is located immediately upstream of the first alpha-PARP gene. Transcription termination occurs in a region approximately 3 kilobases downstream of the beta-PARP gene. The location of the promoter was confirmed by its ability to direct transcription of the bacterial chloramphenicol acetyltransferase gene in insect-form (procyclic) T. brucei. The putative PARP promoter is located in the region between the 3' splice acceptor site (nucleotide position 0) and nucleotide position -196 upstream of the alpha-PARP genes. Regulatory regions influencing the levels of PARP expression may be located further upstream. We conclude that a single promoter, which is located very close to the 3' splice acceptor site of the alpha-PARP genes, directs the transcription of a small, polycistronic, and alpha-amanitin-resistant transcription unit.

Structural requirements in the herpes simplex virus type 1 transactivator Vmw65 for interaction with the cellular octamer-binding protein and target TAATGARAT sequences

Herpes simplex virus type 1 virion protein Vmw65 forms a complex (TRF.C) with TAATGARAT sequences and the cellular transcription factor oct-1, which has been implicated as an intermediate in the activation of gene expression by Vmw65. To examine structural requirements within Vmw65 for this interaction, we analyzed extracts of transfected cells that express mutant Vmw65 proteins by gel retardation assay and identified two regions in the primary sequence of Vmw65 which are necessary for in vitro assembly of TRF.C. The amino-terminal boundary for complex assembly and trans activation mapped between residues 49 and 75. At the carboxyl terminus, deletion as far as residue 388 did not affect in vitro TRF.C assembly, although trans-activating activity was abolished. Deletion beyond residue 388 rapidly impaired the ability of the protein to participate in the TRF.C complex, such that a truncated mutant of 380 residues was completely inactive. These requirements towards the carboxyl terminus overlap a region of strong local sequence similarity between Vmw65 and terminal protein p3 of bacteriophage phi 29. Although substitution of corresponding p3 residues into Vmw65 failed to produce a functional chimera, site-directed mutagenesis within the region of similarity identified a number of single-point mutant proteins which were completely deficient for TRF.C formation. These mutant proteins were also unable to trans activate expression from immediate-early promoters, despite the integrity of the acidic carboxyl terminus. The extreme sensitivity of both TRF.C formation and trans activation to single-residue substitutions within this region of Vmw65 suggests that it is directly involved in the protein-protein or protein-DNA interactions required for assembly of a transcriptional complex containing oct-1.

Synthesis of the herpes simplex virus type 1 trans-activator Vmw65 in insect cells using a baculovirus vector

Vmw65, the Herpes Simplex Virus trans-activator of immediate-early genes, was expressed in insect cells using a recombinant baculovirus expression vector and partially purified. Insect cell-derived Vmw65 was shown to be indistinguishable from authentic Vmw65 present in purified HSV-1 virions based on electrophoretic mobility, immunoreactivity with a monoclonal antibody, and ability to interact with cellular factors to form a protein/DNA complex with oligonucleotides containing a TAATGARAT element.