Transcriptional regulation of a herpes simplex virus immediate early gene is mediated through an enhancer-type sequence

KSHV genome harbors both constitutive and lytically induced enhancers

Kaposi's sarcoma-associated herpesvirus (KSHV) belongs to the gamma-herpesvirus family and is a well-known human oncogenic virus. In infected cells, the viral genome of 165 kbp is circular DNA wrapped in chromatin. The tight control of gene expression is critical for latency, the transition into the lytic phase, and the development of viral-associated malignancies. Distal cis-regulatory elements, such as enhancers and silencers, can regulate gene expression in a position- and orientation-independent manner. Open chromatin is another characteristic feature of enhancers. To systematically search for enhancers, we cloned all the open chromatin regions in the KSHV genome downstream of the luciferase gene and tested their enhancer activity in infected and uninfected cells. A silencer was detected upstream of the latency-associated nuclear antigen promoter. Two constitutive enhancers were identified in the K12p-OriLyt-R and ORF29 Intron regions, where ORF29 Intron is a tissue-specific enhancer. The following promoters: OriLyt-L, PANp, ALTp, and the terminal repeats (TRs) acted as lytically induced enhancers. The expression of the replication and transcription activator (RTA), the master regulator of the lytic cycle, was sufficient to induce the activity of lytic enhancers in uninfected cells. We propose that the TRs that span about 24 kbp region serve as a "viral super-enhancer" that integrates the repressive effect of the latency-associated nuclear antigen (LANA) with the activating effect of RTA. Utilizing CRISPR activation and interference techniques, we determined the connections between these enhancers and their regulated genes. The silencer and enhancers described here provide an additional layer to the complex gene regulation of herpesviruses.IMPORTANCEIn this study, we performed a systematic functional assay to identify cis-regulatory elements within the genome of the oncogenic herpesvirus, Kaposi's sarcoma-associated herpesvirus (KSHV). Similar to other herpesviruses, KSHV presents both latent and lytic phases. Therefore, our assays were performed in uninfected cells, during latent infection, and under lytic conditions. We identified two constitutive enhancers, one of which seems to be a tissue-specific enhancer. In addition, four lytically induced enhancers, which are all responsive to the replication and transcription activator (RTA), were identified. Furthermore, a silencer was identified between the major latency promoter and the lytic gene locus. Utilizing CRISPR activation and interference techniques, we determined the connections between these enhancers and their regulated genes. The terminal repeats, spanning a region of about 24 kbp, seem like a "viral super-enhancer" that integrates the repressive effect of the latency-associated nuclear antigen (LANA) with the activating effect of RTA to regulate latency to lytic transition.

Temporal gene regulation of the channel catfish virus (Ictalurid herpesvirus 1)

To identify promoter regions that impart differential temporal regulation of channel catfish virus (CCV) genes, the transcriptional kinetics of an immediate-early gene and prospective early and late genes were characterized. A cDNA clone, designated IE3C, representing a third immediate-early transcript was identified. The 5' end of the IE3C transcript was mapped to nucleotides 15,368 and 131,043 in the terminal repeat regions of the CCV genome. The full length of the transcript represented by the IE3C clone is 1,412 bp, and it most likely codes for the protein specified by open reading frame (ORF) 12. The putative product of ORF12 contains a consensus RING finger metal binding motif (C3HC4 structure). Temporal expression studies, in conjunction with protein synthesis and DNA replication inhibition, demonstrated that the IE3C transcript belongs to an immediate-early kinetic class, the ORF5 transcript is a member of the early kinetic class, and ORF39 and ORF46 are true late-kinetic-class genes. Additionally, we demonstrated that ORF38 transcription overlaps ORF39 and the products presumably share the same poly(A) signal. The 5' ends of the transcripts encoding ORF38, ORF39, and ORF46 were mapped to nucleotides 44,862, 45,254, and 59,644, respectively, and potential transcriptional control elements were located.

The nucleotide sequence of bovine MHC class II DQB and DRB genes

The nucleotide sequences of most of the exons and parts of the introns of two BoLA-DQB genes and two BoLA-DRB genes have been determined. The structure of these genes is very similar to that of human major histocompatibility complex (MHC) class II genes. The two DQB genes probably represent true alleles. Based on the exons sequenced, both DQB genes and one of the DRB genes seem to be functional. The other DRB gene is a pseudogene; stopcodons are found in the exons encoding the second and transmembrane domain and, furthermore, a 2 base pair (bp) deletion has occurred in the leader exon which places the initiation start codon out of frame. Also in this pseudogene, an almost perfect inverted repeat of 200 bp is found flanking the exon encoding the first domain, which might have been the result of a duplication/inversion event. The sequences presented in this paper do not contain any repetitions. Therefore, DNA fragments containing these sequences can be used as homologous bovine probes in restriction fragment length polymorphism (RFLP) analysis to study disease associations in cattle.

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.

Cloning of the herpes simplex virus ICP4 gene in an adenovirus vector: effects on adenovirus gene expression and replication

To assess the ability of the herpes simplex virus ICP4 protein to complement adenovirus E1a mutants we have constructed an adenovirus type 5 vector containing a temperature-sensitive ICP4 gene, under control of its own promoter, within the E1 region of the genome. The recombinant virus expresses ICP4 in cells which are permissive (293) or nonpermissive (KB and R970-5) for viral replication, and at levels which approximate those obtained in herpes simplex infection. The adenovirus-encoded protein is functional in that it complements an ICP4 deletion mutant of herpes simplex virus; however, it is incapable of complementing adenovirus E1a mutants for viral growth or DNA replication. At the level of activation of gene expression, ICP4 stimulates the expression of the adenovirus E2a gene but not that of other early genes. Our results indicate that ICP4 does not possess all of the functions of the E1a proteins and, furthermore, that adenovirus early genes differ in their susceptibility to heterologous trans-activators.

Molecular analysis of the transcriptional regulatory region of an early baculovirus gene

Transcription of the gene encoding a 35,000-molecular-weight protein (35K protein) from the EcoRI-S region (86.8 to 87.8 map units) of Autographa california nuclear polyhedrosis virus (AcMNPV) occurs early in infection and declines later. The region promoting the gene for the 35K protein, extending from 426 base pairs (bp) upstream to 12 bp downstream from the RNA start site, was linked to the bacterial chloramphenicol acetyltransferase gene (CAT) for analysis. CAT expression was monitored in cells that were transfected with plasmids containing the promoter-CAT fusion as well as cells infected with recombinant viruses containing the chimeric gene inserted into the AcMNPV genome. Mapping of the 5' ends of CAT-specific RNAs indicated that transcription initiated from the proper sites in both assays; moreover, the promoter fragment retained its early activity, despite an alternate location in the viral genome. The 5' boundary of upstream regulatory sequences was determined by constructing deletions of the promoter fragment extending toward the early RNA start site (position +1). In transient assays, a gradual reduction in CAT expression occurred as sequences from positions -426 to -31 were removed. In contrast, promoter deletions from positions -426 to -155 in recombinant viruses exhibited no effect on CAT expression, whereas deletions to position -55 abolished early expression but had no effect on late expression. Late CAT expression was eliminated when deletions to position -4 removed part of the late RNA start site. DNA signals potentiating early transcription were therefore located upstream (between positions -155 and -55) from those involved in late transcription of the gene encoding the 35K protein. Potential consensus sequences for early and late regulatory elements were identified.

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

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

Expression of a truncated viral trans-activator selectively impedes lytic infection by its cognate virus

A virion protein of herpes simplex virus type 1 (HSV-1) specifically and potently activates transcription of the viral immediate early genes. Appropriate function of this protein, termed VP16, depends on an acidic transcriptional activation domain located within the 78 carboxyl-terminal amino acids of the protein. Mutated forms of the protein lacking this acidic domain lose the ability to activate transcription, and can dominantly interfere with the trans-activation function of native VP16 (ref. 1). We have prepared stably transformed mouse L cells that constitutively express a form of VP16 lacking its acidic activating domain. In this report we show that these cells are selectively impaired in their capacity to support the lytic infectious cycle of HSV-1, and that this impairment results from their inability to support immediate early transcription.

Functional dissection of VP16, the trans-activator of herpes simplex virus immediate early gene expression

Mature virions of herpes simplex virus type 1 contain an activating factor that primes transcription from the five virally encoded immediate early (IE) genes. This activator is specified by a 65-kD polypeptide termed VP16. The action of VP16 is mediated through cis-regulatory elements located in regions adjacent to each IE gene. Although VP16 is normally introduced into cells by infecting virions, its trans-activating function can also be observed by cotransfecting cells with a plasmid that encodes VP16 along with a reporter gene driven by IE cis-regulatory sequences. We have used such an assay to examine the function of mutant forms of VP16. Our results provide tentative identification of two domains of VP16 that are crucial to its role in the induction of IE gene expression. One domain is located within the carboxy-terminal 78 amino acids of VP16 and is characterized by its acidity. Another domain, located in a more amino-terminal region of the protein, appears to tailor the specificity of VP16 for IE genes. According to the results presented in this and the accompanying paper, we predict that VP16 achieves IE gene specificity via protein: protein, rather than protein: DNA, interaction.

Evidence of DNA: protein interactions that mediate HSV-1 immediate early gene activation by VP16

The viral genes first expressed upon lytic infection by herpes simplex virus type 1 (HSV-1) encode the five immediate early (IE) proteins. IE gene expression is potently and specifically induced by a virion protein termed VP16. Previous studies have shown that the activating properties of VP16 are IE gene specific and mediated by upstream regulatory elements common to each IE gene. Paradoxically, however, VP16 does not appear to be a sequence-specific DNA-binding protein. To understand the specificity of VP16 activation, we identified the cis-regulatory sequences of an IE gene that mediate VP16 response. Two distinct DNA sequence motifs enable the ICP4 gene to respond to VP16. Biochemical fractionation of nuclear proteins from uninfected cells revealed the existence of cellular proteins that bind directly to each of these VP16 cis-response elements. These observations, in concert with the identification of functional domains of the VP16 protein, lead to the hypothesis that VP16 achieves activation specificity via protein: protein, rather than protein: DNA, interactions.

HSV-1 DNA sequence determining intraperitoneal pathogenicity in mice is required for transcription of viral immediate-early genes in macrophages

The relationship between intraperitoneal (ip) pathogenicity in vivo of herpes simplex virus type 1 (HSV-1) and infection of macrophages (m phi) in vitro was studied. The apathogenic HSV-1 strain HFEM disappeared from the peritoneum of infected mice following ip inoculation, while the pathogenic F strain persisted in the peritoneum and penetrated the mouse nervous system, and eventually the mice died, showing severe neurological signs. When peritoneal m phi were infected in vitro, a direct correlation with pathogenicity in vivo was found with several HSV-1 strains and recombinants. HSV-1 strains (F, KOS, R-M1C1) which were pathogenic for mice by the ip route, induced cytopathic effect (CPE) in m phi in vitro. Strain F transcribed viral immediate-early genes and synthesized viral DNA in m phi that were treated with L-cell conditioned medium (as a source of colony-stimulating factor) prior to infection. Apathogenic HSV-1 strains (HFEM, R-15, R-19) did not cause CPE in m phi. The HFEM strain was already blocked in the transcription of viral alpha genes in the infected m phi, but replicated well in control BSC-1 cells. An intratypic recombinant (R-M1C1), produced by cotransfection of HFEM DNA with a cloned Mlul-Mlul DNA fragment (coordinates 0.7615-0.796) from HSV-1 strain F, that was shown [Becker et al. (1986). Virology 149, 255-259] to have regained partial ip virulence for mice, now transcribed alpha genes, synthesized viral DNA, and induced CPE in m phi. It appears that the viral DNA fragment responsible for ip virulence is involved in tissue-specific recognition of virus by infected m phi, a function necessary for transcription of viral alpha genes.

A complex formed between cell components and an HSV structural polypeptide binds to a viral immediate early gene regulatory DNA sequence

Transcription of HSV immediate early genes is stimulated by a virus structural protein, Vmw65, in a process that requires specific recognition of the sequence TAATGARAT (R = purine). Upon incubation of nuclear extracts of HSV-infected cells with a short DNA fragment containing TAATGARAT, a novel virus-induced protein-DNA complex (named IEC) was detected. Addition of virion extract, containing Vmw65, to nuclear extract from uninfected cells also resulted in the formation of IEC. Vmw65 is a component of IEC, which contains proteins bound specifically to TAATGARAT. Thus, Vmw65 and cellular factors combine to form a sequence-specific DNA-binding complex. This system provides a model for studies of the regulation of inducible cellular genes.

An enhancer element in the short unique region of human cytomegalovirus regulates the production of a group of abundant immediate early transcripts

A 275-bp sequence in the short unique region of human cytomegalovirus (HCMV) strain AD169 contains a series of five imperfect 18-bp repeats with homology to the SV40 and HCMV major immediate early enhancers. Plasmids containing these putative HCMV enhancer sequences linked to the human beta-globin gene were transiently transfected into HeLa cells, and the ability of the HCMV sequences to activate beta-globin transcription was assayed. The repeat-containing region stimulated transcription in a position- and orientation-independent manner, to approximately the same degree as that of the SV40 enhancer. A promoter located immediately 3' to the enhancer in the HCMV genome is active only in the presence of the enhancer sequences. Transcription from this HCMV promoter was analysed by a combination of S1 nuclease protection mapping and Northern blotting. At immediate early times postinfection, at least four extremely abundant differentially spliced mRNAs were detected; these RNAs constitute a previously unknown class of immediate early transcript.

Expression of a cellular gene cloned in herpes simplex virus: rabbit beta-globin is regulated as an early viral gene in infected fibroblasts

We constructed nondefective herpes simplex virus type 1 recombinants bearing the intact rabbit beta-globin gene inserted into the viral gene for thymidine kinase to study the expression of a cellular gene when it is present in the viral genome during lytic viral infections. The globin promoter was activated to high levels during productive infection of Vero cells, giving rise to properly spliced and processed cytoplasmic globin transcripts. Expression of globin RNA occurred with early kinetics, was not affected by blocking viral DNA replication, and was strongly inhibited by preventing viral immediate-early protein synthesis with cycloheximide. These results support the hypothesis that temporal control of herpes simplex virus early gene expression is accomplished by mechanisms that are not restricted to viral promoters. In addition, these data show that a cellular transcript can be correctly processed and can accumulate to high levels during viral infection; this indicates that the mechanisms of virally induced shutoff of host RNA accumulation and degradation of host mRNAs do not depend on sequence-specific differentiation between host and viral RNAs. These findings also suggest that herpesviruses have considerable potential as high-capacity gene transfer vectors for a variety of applications.

DNA sequences which regulate the expression of the pseudorabies virus major immediate early gene

It has been shown previously that the transcription of herpes simplex virus (HSV) immediate early (IE) genes is transactivated by a component of the virus particle. The trans-inducing factor (TIF) is known to be polypeptide Vmw65. Infection with pseudorabies virus (PRV), a related herpesvirus, does not increase expression from HSV IE regulatory sequences (W. Batterson and B. Roizman, 1983, J. Virol. 46, 371-377). To examine the control of the PRV IE gene and possible sequence specificity of a TIF, the 5' terminus of the PRV major IE transcript was mapped and hybrid plasmids containing PRV upstream sequences linked to the HSV-1 TK gene were constructed. Gene expression under the control of PRV IE or HSV-1 IE gene 3 upstream regions were compared using transient expression assays. It was found that infection with uv-irradiated PRV did not stimulate expression from PRV IE or from HSV-1 IE gene 3 upstream regions, indicating that PRV did not possess an effective TIF. Infection with uv-treated HSV-1, or cotransfection with a plasmid which encodes Vmw65, stimulated expression from both PRV and HSV IE gene upstream regions. The nucleotide sequence of the 5' end of the PRV transcript and its upstream region was determined. This region was, in overall structure, unlike the upstream regions of HSV IE genes but showed a strong similarity to the enhancers of human and murine cytomegaloviruses (HCMV and MCMV). In particular, a reiterated 15-bp element of the PRV upstream region was homologous to a conserved, repeated sequence element found in both HCMV and MCMV enhancer regions and was also related to the "TAATGARATTC" motif found upstream of all HSV IE genes. Thus a conserved sequence element occurs upstream of IE genes in four herpesviruses with different genome structures and diverse biological properties.

Interspersed Homologous DNA of Autographa californica Nuclear Polyhedrosis Virus Enhances Delayed-Early Gene Expression

The five regions of homologous DNA which are interspersed in the genome of the baculovirus Autographa californica nuclear polyhedrosis virus increased the expression of a delayed-early gene of this virus. Although this activity was first observed as a 10-fold trans effect, the homologous region 5 ( hr 5) enhanced the expression of linked genes 1,000-fold. The hr 5 enhancer also exhibited the other characteristics associated with viral enhancer elements, including orientation independence and the abilities to function at a distance from the linked promoter, to regulate heterologous promoters, and to increase the number of RNA polymerase molecules transcribing the linked genes. The expression of the immediate-early regulatory gene was not enhanced by cis -linked hr 5, although the enhancer function may require the immediate-early regulatory gene product. The hr 5 enhancer was relatively insensitive to competition by an excess of enhancer molecules. The nucleotide sequence of hr 5 revealed two different conserved repeats separated by nonhomologous DNA. Deletion analysis of the hr 5 enhancer indicated that a 30-base-pair inverted repeat was essential for enhancer function.

Activation of the AIDS retrovirus promoter by the cellular transcription factor, Sp1

The nature and position of transcriptional control elements responsible for the expression of genes encoded by the retrovirus associated with acquired immune deficiency syndrome (AIDS) have not been precisely defined. In this study it is shown that the mammalian Sp1 transcription factor binds to promoter sequences within the AIDS retrovirus long terminal repeat (LTR) and activates RNA synthesis five- to eightfold in reconstituted reactions in vitro. Experiments in which regions of DNA were protected from added reagents by specifically bound proteins (footprinting) indicated that the upstream promoter region of the AIDS virus LTR lies between -45 and -77 (relative to the RNA start site, +1) and contains three tandem, closely spaced SP1 binding sites of variable affinity. Base-substitution mutations targeted to one or all three Sp1 binding sites were found both to eliminate the binding of Sp1 and to cause up to a tenfold reduction in transcriptional efficiency in vitro. These findings suggest that one important component of the AIDS virus transcriptional control region interacts with a cellular transcription factor, Sp1, and that this factor must function in conjunction with transcriptional elements located downstream of the RNA cap site to mediate the response of the LTR to viral trans-activation.

Sp1 binds to promoter sequences and activates herpes simplex virus 'immediate-early' gene transcription in vitro

During a herpes simplex virus (HSV-1) lytic infection, three classes of viral genes are transcribed in a temporally regulated manner. The HSV-1 'immediate-early' (IE) promoter sequences contain multiple copies of a hexanucleotide sequence, GGGCGG, known as a GC box, and one or more copies of an 11-base pair (bp) conserved A + T-rich element, designated TAATGARAT. The TAATGARAT elements are thought to mediate the trans-activation of IE RNA synthesis by a virion-associated protein(s), and the flanking G + C-rich sequences appear both to potentiate this induction and to direct IE promoter activity in vivo. The similarity of the herpesvirus GC box repeats to those of the simian virus 40 (SV40) early promoter prompted the in vitro analysis of HSV IE transcription reported here. We show that the mammalian gene-specific transcription factor Sp1 binds to eight distinct regions of the HSV short terminal repeat and stimulates transcription 25-fold from the divergent IE-3 (ICP-4) and IE-4/5 promoters.

Two distinct transcription factors bind to the HSV thymidine kinase promoter in vitro

We have characterized an in vitro transcription system derived from uninfected HeLa cells that accurately initiates RNA synthesis at the herpes virus thymidine kinase (TK) promoter. Analysis of linker-scanning, single-site, and promoter-inversion mutants reveals that the TK upstream elements previously mapped in vivo are accurately recognized in vitro. A protein fraction required for TK transcription in reconstitution experiments was found to contain multiple protein species that bind specifically to the TK promoter. DNAase I footprint experiments with wild-type and mutant promoters reveal that the TK upstream elements contain three distinctive protein binding sites, two of which appear to be recognized by the Sp1 transcription factor and one which interacts with a cellular protein that binds to "CCAAT" sequences. Optimal expression of the thymidine kinase gene appears to require the coordinate interaction of these two types of transcription factors with the three upstream elements of the promoter.

Simian virus 40 enhancer increases RNA polymerase density within the linked gene

Enhancers are regulatory DNA elements, usually about 200 base pairs (bp) long, which are able to stimulate transcription of linked genes in eukaryotic cells. This activation can be exerted over large distances, and from a position 5' or 3' to the gene. Enhancers have been identified in viral genomes and cellular genes. Using a transient expression assay, we have analysed transcription of the rabbit beta-globin gene and the thymidine kinase gene from herpes simplex virus with and without a simian virus 40 (SV40) enhancer. S1 nuclease mapping shows a high level of specific transcripts when the genes are linked to the enhancer. To determine whether this increased number of transcripts is due to a higher transcription rate, or perhaps to a shift from nonspecific to specific initiation, we have performed run-on transcription assays with isolated nuclei. Our results, presented here, demonstrate that the SV40 enhancer increases the RNA polymerase density within the linked gene. Therefore, enhancers apparently increase the rate of transcription initiation without influencing the specificity of initiation.

Identification of herpes simplex virus DNA sequences which encode a trans-acting polypeptide responsible for stimulation of immediate early transcription

Herpes simplex virus (HSV) immediate early (IE) transcription is known to be stimulated by a structural component of the virion which interacts, either directly or indirectly, with specific regulatory sequences located far upstream from IE messenger RNA 5'-termini. The aim of the work described in this paper is the mapping and identification of the virion component. Cloned HSV DNA fragments derived from various parts of the genome were cotransfected into BHK cells together with chimaeric plasmids which contained the thymidine kinase gene under IE control. Stimulation of thymidine kinase synthesis was elicited by cloned EcoRIi (0.63 to 0.72 map units), BamHIf (0.64 to 0.69) or EcoRIb (0.72 to 0.87). Cloned BamHIf had the same specificity as the virion component, since it stimulated thymidine kinase expression only from chimaeric plasmids which contained functional IE-specific regulatory sequences. The effect of EcoRIb was not confined to plasmids with IE-specific regulatory regions, suggesting a more general stimulatory role for one or more of the polypeptides encoded by this fragment. A subclone containing a 2.7 X 10(3) base-pair fragment of BamHIf (pMC1) was active in the cotransfection assay, and the effect was abolished by an eight base-pair insertion into the middle of this fragment. The only polypeptide known to map entirely within the HSV genome region defined by pMC1 was identified as the major tegument species Vmw65. The results therefore suggest that Vmw65 is the virion component which trans-activates HSV IE transcription.

Identification of the herpes simplex virus type 1 gene encoding the dUTPase

The dUTPase gene of herpes simplex virus has been identified using a novel approach. The upstream regulatory sequences, or the promoter and upstream regulatory sequences, of the immediate-early gene Vmw175 (ICP4) were inserted in front of genes mapping in the region 0.69 to 0.70 map units of the virus genome to enhance transient gene expression in a transfection assay. One clone, containing a gene specifying a 1.5-kb mRNA, induced significant amounts of virus-specific dUTPase activity. The enzyme activity was abolished by insertion of a HindIII linker into the KpnI site within the coding sequences of this gene. The results show that the enzyme is virus coded and that 1.5-kb mRNA specifies the dUTPase.

A tissue-specific transcription enhancer element in the human immunoglobulin lambda light chain locus

An 8.0-kb EcoRI fragment of the human immunoglobulin (Ig) lambda light chain locus carrying the Ke-Oz- and Ke-Oz+ constant region genes and flanking sequences was studied for the presence of a transcriptional enhancer. Two types of assays were used. In the first, we measured the ability of recombinant plasmids carrying the 8.0-kb Ig fragment covalently linked to the aminoglycoside phosphotransferase (aph) gene to transform mouse myeloma or mouse fibroblast cells to geneticin resistance. In the second, we used RNA spot and Northern blot hybridization analyses to determine the relative levels of aph specific RNA transiently expressed after DNA transfection. In fibroblast cells, the transformation frequencies were independent of the presence of the Ig fragment in the vector and there was no difference in the level of transient expression of the aph gene. In myeloma cells, the Ig fragment enhanced at least 10-fold both the number of transformants and the level of aph gene expression over that obtained with vector alone. These results indicate the presence of a tissue-specific transcriptional enhancer in the 8.0-kb EcoRI fragment of the human Ig C lambda locus.

Effects of orientation and position on the activity of a herpes simplex virus immediate early gene far-upstream region

It has previously been shown that a far-upstream region of the herpes simplex virus immediate early (IE) gene 3 increases the expression of a linked thymidine kinase (TK) gene and also contains sequences which respond to stimulation of transcription by a virion component. The effects of altering the orientation and distance of the far-upstream region with respect to the normal IE gene 3 promoter are described. Reversal of the orientation whilst retaining the normal position of the far-upstream region did not affect its activity, but placing it downstream from the TK gene abolished any detectable effect. When the far-upstream region was separated from the promoter by insertion of Escherichia coli DNA fragments (approximately 1000 base pairs), its activity was reduced but not prevented. A similar effect was observed for unstimulated expression of TK and stimulated expression in the presence of the virion component. The IE gene 3 far-upstream region therefore resembles enhancer sequences in some respects but also shows significant differences.