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

Analysis of human papillomavirus type 16 late mRNA 3' processing signals in vitro and in vivo

In the human papillomavirus type 16 genome, three late mRNA putative 3' processing signals, designated LP1, LP2, and LP3, are located downstream of the late coding region. Our results show, both in vitro and in vivo, that in HeLa cells, the LP2 signal functions. Thus, the restriction in human papillomavirus type 16 late-gene expression observed in HeLa cells and other nondifferentiated epithelial cells is not achieved by regulation of late mRNA poly(A) site usage. Interestingly, alteration of three nucleotides in the GU-rich downstream sequence element converts the nonfunctional LP1 to an efficient 3' processing site, suggesting that LP1 may function in cell types other than HeLa, such as differentiated keratinocytes. Our transfection studies have identified a negative regulatory element located immediately upstream of the late mRNA 3' processing signals; this element was not associated with any alteration in 3' processing and may act as an mRNA instability element.

The promoter structure and complete sequence of the gene encoding the rabbit erythroid cell-specific 15-lipoxygenase

We report the isolation and complete sequence of the gene encoding the rabbit erythroid-cell-specific 15-lipoxygenase (RBC 15-LOX), containing 14 exons spanning 8.0 kb. The transcription start point was mapped by S1 nuclease-protection experiments and comparison with the sequence of the RBC 15-LOX mRNA, as defined previously by primer extension experiments. The promoter contains a TATA-like motif, but no CCAAT motif in the canonical position, and lies within a 'CpG-rich island'. Functional analysis of the immediate 5'-flanking DNA by transfection experiments shows that a 150 nucleotide (nt) 5' fragment linked to the chloramphenicol acetyltransferase gene acts as a functional promoter in both erythroid and nonerythroid cell lines and responds in an erythroid-specific manner to the enhancer from the Friend murine leukaemia virus long terminal repeat, whereas a 40-nt fragment is inactive. Intron 7 contains eight copies of a 54-nt repeat containing a region with homology to the simian virus 40/immunoglobulin gene enhancers.

Herpes simplex virus Vmw65-octamer binding protein interaction: a paradigm for combinatorial control of transcription

The transcriptional status of a given viral or cellular gene is determined both by the availability of functional transcription factors and by the combination and spatial arrangement of the cis-acting elements to which they bind. While differential gene expression can be achieved to some extent by the interaction of different factors with different genes it is clear that in some cases the same factor is required for the regulation of genes that are not coordinately expressed. How a transcription factor achieves selective function in the absence of selective binding is a question that remains largely unanswered. The recent advances in understanding how both protein-protein and protein-DNA interactions are required to mediate the induction of herpes simplex virus immediate early (HSV IE) gene expression have highlighted a novel mechanism for combinatorial control of transcription which has significant implications for the differential control of cellular gene expression.

c-Ha-ras gene bidirectional promoter expressed in vitro: location and regulation

Increased transcriptional activity of the c-Ha-ras gene product is correlated with induction of several important human tumor types. For this reason, we have investigated the nature of the c-Ha-ras promoter and the factors that regulate its expression. Using S1 and primer extension analysis of c-Ha-ras RNA from EJ cells, we have identified 18 initiation sites within an upstream exon (exon -1) whose 3' end (the donor splice site [D]) is located 1,105 base pairs (bp) upstream of the ATG codon. The furthest-upstream initiation site is located -191 bp relative to D, and the furthest downstream is located -16 bp relative to D. Transient expression assays, in which a series of mutants spanning this region were ligated to a promoterless chloramphenicol acetyltransferase vector, functionally confirmed the position and extent of this promoter. Mutational analysis further located a 47-bp element located between -243 and -196 relative to D that up-regulated transcriptional activity of the promoter region by 20- to 40-fold. This region contained both a GC box known to bind SP1 and a CCAAT box. Insertion of a simian virus 40 enhancer 5' to the promoter up-regulated transcription from each initiation site by approximately 10- to 20-fold. We have also localized, both by chloramphenicol acetyltransferase assay and by S1 analysis, a strong promoter operating in the direction opposite that of the gene and originating immediately 5' to the 47-bp regulatory region. The reverse promoter was found to have nine initiation sites between -248 and -278 relative to D.

c-Ha-ras gene bidirectional promoter expressed in vitro: location and regulation

Increased transcriptional activity of the c-Ha-ras gene product is correlated with induction of several important human tumor types. For this reason, we have investigated the nature of the c-Ha-ras promoter and the factors that regulate its expression. Using S1 and primer extension analysis of c-Ha-ras RNA from EJ cells, we have identified 18 initiation sites within an upstream exon (exon -1) whose 3' end (the donor splice site [D]) is located 1,105 base pairs (bp) upstream of the ATG codon. The furthest-upstream initiation site is located -191 bp relative to D, and the furthest downstream is located -16 bp relative to D. Transient expression assays, in which a series of mutants spanning this region were ligated to a promoterless chloramphenicol acetyltransferase vector, functionally confirmed the position and extent of this promoter. Mutational analysis further located a 47-bp element located between -243 and -196 relative to D that up-regulated transcriptional activity of the promoter region by 20- to 40-fold. This region contained both a GC box known to bind SP1 and a CCAAT box. Insertion of a simian virus 40 enhancer 5' to the promoter up-regulated transcription from each initiation site by approximately 10- to 20-fold. We have also localized, both by chloramphenicol acetyltransferase assay and by S1 analysis, a strong promoter operating in the direction opposite that of the gene and originating immediately 5' to the 47-bp regulatory region. The reverse promoter was found to have nine initiation sites between -248 and -278 relative to D.

Purification of a set of cellular polypeptides that bind to the purine-rich cis-regulatory element of herpes simplex virus immediate early genes

Expression of herpes simplex virus type 1 (HSV1) immediate early (IE) genes is activated by a polypeptide component of the mature virion termed viral protein 16 (VP16). Stimulation of IE expression by VP16 operates via two cis-regulatory sequences: TAATGARAT, and the purine-rich hexanucleotide sequence GCGGAA. VP16 does not bind directly to either of the IE cis-regulatory sequences. Rather, these elements appear to represent binding sites for host cell proteins. Herein, we report the purification of a host cell factor that binds to the GCGGAA motif. We show further that this factor is capable of binding in vitro to an oligomerized form of the hexanucleotide sequence GAAACG, which is common to a variety of virus- and interferon-inducible genes. The GAAACG repeats of interferon- and virus-inducible genes, and the GA-rich repeats of HSV1 IE genes confer similar functional properties when appended to the promoter of a heterologous gene. These observations raise the possibility that HSV1 may activate its IE genes in a manner that exploits one of the components used by mammalian cells to combat virus infection.

Overlapping octamer and TAATGARAT motifs in the VF65-response elements in herpes simplex virus immediate-early promoters represent independent binding sites for cellular nuclear factor III

Expression of the immediate-early (IE) genes of herpes simplex virus (HSV) is specifically stimulated by a 65-kilodalton virion transcription factor (VF65 or VP16) that is introduced as a component of infecting virions. In both the IE175(ICP4) and IE110(ICP0) promoters, this activation requires an upstream cis-acting target response element that contains a single TAATGARAT consensus element. Furthermore, many HSV IE TAATGARAT elements overlap with ATGCTAAT octamer motifs that are similar to the OTF-1-binding sites found in both immunoglobulin and histone H2b genes and to the nuclear factor III (NFIII)-binding site within the adenovirus type 2 origin of DNA replication. Purified HeLa cell NFIII protein proved to form specific DNA-protein complexes with several upstream regions from both the IE110 and IE175 promoters, and this interaction was subject to efficient competition with an adenovirus type 2 DNA fragment containing an intact NFIII-binding site. Surprisingly, the NFIII protein bound to synthetic oligonucleotides containing only the TAATGARAT consensus elements as well as to those containing the ATGCTAAT octamer sequence, although the former exhibited lower affinity and gave complexes with slightly different electrophoretic mobility. The ATGCTAAT oligonucleotide also competed more efficiently than the TAATGARAT sequence itself for binding to a TAATGARAT probe, indicating that the same protein species binds to both sites. The oligonucleotides also formed novel supershifted complexes with lysed virion proteins, but only in the presence of a crude nuclear extract and not with affinity-purified NFIII alone. We conclude that the cellular NFIII protein can recognize both the ATGCTAAT and TAATGARAT elements independently but that only the interaction with TAATGARAT represents an intermediate step in the transcriptional stimulation of IE genes by the HSV virion factor.

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

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

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

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

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

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

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

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

GATAAG; a cis-control region binding an erythroid-specific nuclear factor with a role in globin and non-globin gene expression

An erythroid-specific nuclear protein factor binds to a sequence motif (GATAAG) which is present in the promoter region of the mouse alpha and beta major globin genes, and in the erythroid-specific promoter of the human porphobilinogen deaminase (PBG-D) gene. The protein activity is conserved across species, being found in mouse erythroleukaemia (MEL) cells, chicken erythrocytes, the human erythroid K562 and KMOE cell lines, but not in a variety of non-erythroid mouse tissues or in HeLa cells. Functional analysis of this element in the alpha globin gene promoter by stable transfection experiments show that the GATAAG motif resides in a 68 bp sequence which has a stimulatory effect on transcription in mouse erythroleukaemia but not fibroblast cells. The GATAAG motif is conserved in the promoters and 3' enhancers of a variety of globin and non-globin genes implying that it is a cis-element involved in the tissue-specific up-regulation of several genes that are co-expressed during erythroid cell differentiation.

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)

Adenovirus vector expressing functional herpes simplex virus ICP0

ICP0, one of the five immediate-early (IE) gene products of herpes simplex virus (HSV), is a potent activator of transcription. To assess the biological activities of ICP0 and to explore its mechanisms of action, two helper-independent recombinant adenoviruses were constructed. In each recombinant, the E1 region was substituted with the ICP0-encoding genomic segment under the control of either the adenovirus major late promoter (MLP-0) or the HSV IE-0 promoter (0PRO-0). Infection of HeLa cells or 293 cells (a human embryo kidney cell line expressing adenovirus 5 E1a and -b functions) with the MLP-0 recombinant results in the synthesis of more IE-0 mRNA and ICP0 protein than did infection with the 0PRO-0 recombinant. Although 293 cells infected with MLP-0 accumulate 5- to 10-fold more IE-0 mRNA late in the infection than cells infected with HSV, the level of the protein product, ICP0, increased only slightly. In 293 cells, both recombinants could replicate, albeit at a slower rate and with lower final yields than wild-type adenovirus. Neither virus replicates its DNA in HeLa cells, and thus ICP0 cannot substitute for adenovirus E1a; however, the level of ICP0 that accumulates in MLP-0-infected HeLa cells was comparable to that of HSV-infected HeLa cells. In a functional test, we demonstrated that the adeno-ICP0 recombinant viruses can transactivate a transfected TK-CAT cassette, indicating that the ICP0 is biologically active.

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

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

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

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

Components required for in vitro cleavage and polyadenylation of eukaryotic mRNA

We have studied in vitro cleavage/polyadenylation of precursor RNA containing herpes simplex virus type 2 poly A site sequences and have analyzed four RNA/protein complexes which form during in vitro reactions. Two complexes, A and B, form extremely rapidly and are then progressively replaced by a third complex, C which is produced following cleavage and polyadenylation of precursor RNA. Substitution of ATP with cordycepin triphosphate prevents polyadenylation and the formation of complex C however a fourth complex, D results which contains cleaved RNA. A precursor RNA lacking GU-rich downstream sequences required for efficient cleavage/polyadenylation fails to form complex B and produces a markedly reduced amount of complex A. As these GU-rich sequences are required for efficient cleavage, this establishes a relationship between complex B formation and cleavage/polyadenylation of precursor RNA in vitro. The components required for in vitro RNA processing have been separated by fractionation of the nuclear extract on Q-Sepharose and Biorex 70 columns. A Q-Sepharose fraction forms complex B but does not process RNA. Addition of a Biorex 70 fraction restores cleavage activity at the poly A site but this fraction does not appear to contribute to complex formation. Moreover, in the absence of polyethylene glycol, precursor RNA is not cleaved and polyadenylated, however, complexes A and B readily form. Thus, while complex B is necessary for in vitro cleavage and polyadenylation, it may not contain all the components required for this processing.

Negative and positive regulation by a short segment in the 5'-flanking region of the human cytomegalovirus major immediate-early gene

To analyze the significance of inducible DNase I-hypersensitive sites occurring in the 5'-flanking sequence of the major immediate-early gene of human cytomegalovirus (HCMV), various deleted portions of the HCMV immediate-early promoter regulatory region were attached to the chloramphenicol acetyltransferase (CAT) gene and assayed for activity in transiently transfected undifferentiated and differentiated human teratocarcinoma cells, Tera-2. Assays of progressive deletions in the promoter regulatory region indicated that removal of a 395-base-pair portion of this element (nucleotides -750 to -1145) containing two inducible DNase I sites which correlate with gene expression resulted in a 7.5-fold increase in CAT activity in undifferentiated cells. However, in permissive differentiated Tera-2, human foreskin fibroblast, and HeLa cells, removal of this regulatory region resulted in decreased activity. In addition, attachment of this HCMV upstream element to a homologous or heterologous promoter increased activity three- to fivefold in permissive cells. Therefore, a cis regulatory element exists 5' to the enhancer of the major immediate-early gene of HCMV. This element negative modulates expression in nonpermissive cells but positively influences expression in permissive cells.

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.

Herpes simplex virus regulatory elements and the immunoglobulin octamer domain bind a common factor and are both targets for virion transactivation

Functional upstream activator sequences (TAATGARAT motifs) of herpes simplex virus immediate-early genes were identified and shown both to bind a factor (TRF) present in uninfected HeLa cells and to confer inducibility by the virus regulatory protein, Vmw65, on a normally nonresponsive promoter. Point-mutation analyses demonstrated binding specificity and correlated binding with Vmw65 induction. Furthermore, the octamer domains of the adenovirus DNA replication origin, the histone H2B, and the immunoglobulin light chain genes bound and competed for TRF. The immunoglobulin octamer also conferred Vmw65 inducibility on the TK promoter. In addition, a modified form of TRF was specifically detected in infected cells. We conclude that TRF is similar or identical to the previously described octamer binding protein and is likely to be the target for coordinate induction of immediate-early gene expression by Vmw65.

Negative and positive regulation by a short segment in the 5'-flanking region of the human cytomegalovirus major immediate-early gene

To analyze the significance of inducible DNase I-hypersensitive sites occurring in the 5'-flanking sequence of the major immediate-early gene of human cytomegalovirus (HCMV), various deleted portions of the HCMV immediate-early promoter regulatory region were attached to the chloramphenicol acetyltransferase (CAT) gene and assayed for activity in transiently transfected undifferentiated and differentiated human teratocarcinoma cells, Tera-2. Assays of progressive deletions in the promoter regulatory region indicated that removal of a 395-base-pair portion of this element (nucleotides -750 to -1145) containing two inducible DNase I sites which correlate with gene expression resulted in a 7.5-fold increase in CAT activity in undifferentiated cells. However, in permissive differentiated Tera-2, human foreskin fibroblast, and HeLa cells, removal of this regulatory region resulted in decreased activity. In addition, attachment of this HCMV upstream element to a homologous or heterologous promoter increased activity three- to fivefold in permissive cells. Therefore, a cis regulatory element exists 5' to the enhancer of the major immediate-early gene of HCMV. This element negative modulates expression in nonpermissive cells but positively influences expression in permissive cells.

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

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

Herpes simplex virus immediate-early promoters are responsive to virus and cell trans-acting factors

The promoters for each of the immediate-early genes from herpes simplex virus type 1 were cloned and fused to a chloramphenicol acetyltransferase cassette. These chimeric genes were used as targets in a transient expression assay to determine how the immediate-early gene products ICP4 and ICP0 and the virion-associated stimulatory protein Vmw65 affected their expression in HeLa and Vero cells. The basal level of expression from these cassettes differed significantly depending on the extent of 5'-flanking sequence and the cell line that served as host. The promoters from IE-4 and IE-0 behaved in a qualitatively similar fashion independent of the host cell. However, the promoter for ICP27 had a unique response pattern: in Vero cells it acted as an alpha gene promoter, whereas in HeLa cells its response was more like that of a beta gene promoter. The promoter sequences for ICP22 and ICP47 behaved as the IE-4 and IE-0 promoters did in HeLa cells, but their response to the effector molecules in Vero cells was unlike that of other alpha gene promoters we have studied. Evidence is also presented for a role for ICP27 in autoregulation.

Transcriptional enhancer activity in the variable tandem repeat DNA sequence downstream of the human Ha-ras 1 gene

A short term transfection technique using the chloramphenicol acetyltransferase gene as an assay system has been employed to examine the presence of transcriptional regulatory sequences within the variable tandem repeat (VTR) DNA sequence located downstream of the human Ha-ras1 gene. Here we find that the VTR sequences possess an endogenous enhancer activity of both the normal and the T24 mutant Ha-ras1 gene.

Electric field-mediated gene transfer (electroporation) into mouse Friend and human K562 erythroleukemic cells

Electroporation, the technique of electric field mediated gene transfer, was evaluated as a means of introducing and expressing genes into mouse Friend and human K562 erythroleukemic cells. Long-term (stable) gene expression in both Friend and K562 cells was measured using the recombinant plasmid Homer 6, which carries the aminoglycoside phosphotransferase (aph) gene as a selectable marker under the transcriptional control of the Moloney murine sarcoma virus long terminal repeat promoter/enhancer sequences. Parameters such as the DNA concentration, the initial field strength, the concentration of recipient cells, and the preselection expression time were examined to obtain optimal transfection frequencies. Short-term (transient) expression was also examined using the plasmid pLW4, which carries the chloramphenicol acetyltransferase gene under the transcriptional control of herpes simplex virus immediate early 5 gene promoter/enhancer sequences. Conditions that gave maximal stable transformation frequency were similar to those giving highest transient gene expression in the mouse and human erythroleukemic cell lines. Under optimal conditions, electroporation gave about ten times higher transfection frequencies and levels of transient expression for both types of cells when compared with the calcium phosphate technique. Because both Friend and K562 cells can be induced to differentiate in vitro, measurement of transient or stable expression levels for genes introduced into these cells may prove to be useful in the study of developmental regulation of genes from the erythroid pathway.

Comparison of upstream sequence requirements for positive and negative regulation of a herpes simplex virus immediate-early gene by three virus-encoded trans-acting factors

Using a short-term cotransfection system with recombinant chloramphenicol acetyltransferase (CAT) target genes and intact genes for regulatory proteins, we previously demonstrated that expression from the promoter-regulatory region of the gene for the immediate-early 175,000-molecular-weight (IE175K) protein of herpes simplex virus type 1 was subject to trans-acting effects by three different virus-encoded components. In the present work we have attempted to delineate the upstream cis-acting requirements within the IE175K promoter-regulatory region for stimulation by the late structural protein Vmw65, stimulation by the IE110K protein, and repression by its own gene product, the IE175K protein. Our results augment previous reports of others by demonstrating that a construct containing only the single TAATGARAT consensus sequence, TAATGGAAT, between -115 and -106 was efficiently induced by Vmw65. Deletion to -108 effectively abolished the response to Vmw65. However, this latter construct remained responsive to IE110K stimulation and was induced as efficiently as the parental construct which contained sequences to -1900. Furthermore, not only basal levels of expression, but also Vmw65 activation of the parental construct and deletion mutants delta 380, delta 330, delta 300, and delta 160 and IE110K-activated expression of the delta 108 construct were all subject to dominant repression by the IE175K protein. Finally, we show that expression from each of the deletions was open to stimulation by linkage to the simian virus 40 enhancer region. Enhancer-stimulated expression from each construct, including the -108 deletion, was efficiently repressed by the IE175K protein. In contrast, expression from the simian virus 40 enhancer when linked to its own promoter was unaffected by IE175K. These results place sequence requirements for both IE110K stimulation and IE175K autoregulation within the minimal promoter region -108 to +30, separate from the major requirements for Vmw65 activation located further upstream.

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

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

Promotor and enhancer like activity at the 5'-end of normal and T24 Ha-ras1 genes

We have used a short-term transfection technique, in which we monitor the ability of DNA fragments to induce the expression of the chloramphenicol acetyltransferase (CAT) gene in rat 208F fibroblast cells. Using appropriate vectors we have assayed for promoter or enhancer activity of the 0.8 kb SstI fragment located within the 5'-flanking sequences of the first coding exon of the human T24 and normal Ha-ras1 genes. We find that this fragment contains promoter and enhancer activities in both the normal and the T24 Ha-ras1 gene.

Analysis of DNA sequences which regulate the transcription of herpes simplex virus immediate early gene 3: DNA sequences required for enhancer-like activity and response to trans-activation by a virion polypeptide

The far upstream region of herpes simplex virus (HSV) immediate early (IE) gene 3 has previously been shown to increase gene expression in an enhancer-like manner, and to contain sequences which respond to stimulation of transcription by a virion polypeptide, Vmw65. To analyse the specific DNA sequences which mediate these functions, sequential deletions from each end of the far upstream region were made. The effects of the deletions on transcription in the absence or presence of the Vmw65 were measured by use of a transient expression assay. The enhancer-like activity was due to three separable elements, whereas two additional DNA regions were involved in the response to Vmw65. One of the responding elements corresponded to an AT-rich consensus (TAATGARATTC, where R = purine) present in all IE gene far upstream regions, and the other was a GA-rich sequence also present in IE genes 2 and 4/5. The TAATGARATTC element could mediate responsiveness to Vmw65 but it was fully active only in the presence of the GA-rich element. The GA-rich element was unable to confer a strong response alone but could activate an otherwise nonfunctional homologue of TAATGARATTC.