Activation of adenovirus promoters by the adenovirus E1A protein in cell-free extracts

Transcription stimulation of the adenovirus type 12 E1a gene in vitro by the 266-amino-acid E1A protein

We previously showed that the 13S but not the 12S mRNA product of the E1a gene of the highly oncogenic type 12 adenovirus (Ad12) stimulates the expression of its own gene. In this study, the mechanism for the autoregulation of the Ad12 E1a gene was investigated in vitro. The 266-amino-acid E1A protein of Ad12 was synthesized in yeast cells and purified as a 57-kDa polypeptide. The purified Ad12 E1A protein stimulated transcription from the proximal promoter of its own gene but had almost no effect on that from the distal promoter. A 35-bp upstream region including a TATA box for the proximal promoter seemed to be sufficient for transcription stimulation by the E1A protein. The Ad12 E1A protein formed a complex with a TATA box-binding protein (TBP), as does the E1A protein of nononcogenic Ad serotypes. Moreover, the E1A protein significantly reduced the binding of TBP to a TATA sequence, while it did not affect the DNA-binding activity of nuclear factor I, a stimulatory protein of the distal transcription of the Ad12 E1a gene. These results suggest that the 13S mRNA product of the Ad12 E1a gene regulates the transcription of its own gene by modulating the activity of TBP.

Expression, purification, and functional characterization of adenovirus 5 and 12 E1A proteins produced in insect cells

The 12 S and 13 S E1A cDNAs from both the Adenovirus (Ad) nononcogenic type 5 and the oncogenic type 12 were overexpressed in an insect cell/baculovirus system. Upon infection of Spodoptera frugiperda cells, the production of E1A proteins reached a level of about 15 micrograms/10(6) cells. The E1A proteins are highly soluble and apparently are processed authentically. They are readily recognized by various antibodies and display phosphorylation patterns similar to those of E1A proteins synthesized in mammalian cells. Single-step immunoaffinity chromatography was used to purify the Ad5 E1A proteins to near homogeneity under nondenaturing conditions. The Ad5 and Ad12 E1A proteins are able to form complexes with the retinoblastoma susceptibility gene product (Rb) and other cellular proteins. Interestingly, the presence of a cellular extract seems to be a prerequisite for association between highly purified E1A and Rb polypeptides.

A purified adenovirus 289-amino-acid E1A protein activates RNA polymerase III transcription in vitro and alters transcription factor TFIIIC

We have previously demonstrated that a purified bacterially synthesized E1A 289-amino-acid protein is capable of stimulating transcription from the promoters of genes transcribed by RNA polymerase II in vitro (R. Spangler, M. Bruner, B. Dalie, and M. L. Harter, Science 237:1044-1046, 1987). In this study, we show that this protein is also capable of transactivating in vitro the adenovirus virus-associated (VA1) RNA gene transcribed by RNA polymerase III. Pertinent to the transcription of this gene is the rate-limiting component, TFIIIC, which appears to be of two distinct forms in uninfected HeLa cells. The addition of an oligonucleotide containing a TFIIIC binding site to HeLa whole-cell extracts inhibits VA1 transcription by sequestering TFIIIC. However, the addition of purified E1A to extracts previously challenged with the TFIIIC oligonucleotide restores the level of VA1 transcription. When included in the same reaction, an E1A-specific monoclonal antibody reverses the restoration. Incubation of purified E1A with either HeLa cell nuclear or whole-cell extracts alters the DNA-binding properties of TFIIIC as detected by gel shift assays. This alteration does not occur if E1A-specific antibody and E1A protein are added simultaneously to the extract. In contrast, the addition of this antibody to extracts at a later time does not reverse the alteration observed in the TFIIIC binding activities. Never at any time did we note the formation of novel TFIIIC-promoter complexes after the addition of E1A to nuclear extracts. These results clearly establish that E1A mediates its effect on VA1 transcription through TFIIIC in a very rapid yet indirect manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct interaction between adenovirus E1A protein and the TATA box binding transcription factor IID

Adenovirus E1A has long been known to activate/repress cellular and viral transcription. The transcriptional activity of nuclear extracts was depleted after chromatography on immobilized E1A protein columns that specifically retained the transcription factor (TF) IID. Stronger direct interactions between E1A and human TFIID than between E1A and yeast TFIID suggest that the unique sequences of the human protein may be involved. We have demonstrated that this interaction occurs directly between bacterially produced E1A and bacterially produced human TFIID in a protein blot assay. We propose that E1A protein may transduce regulatory signals from upstream activators to basal elements of the transcriptional machinery by contacting TFIID.

Adenovirus E1A protein activates transcription of the E1A gene subsequent to transcription complex formation

The mechanism of transcriptional activation of the adenovirus E1A and E3 genes by E1A protein during infection was examined by using transcription-competition assays. Infection of HeLa cells with one virus led to inhibition of mRNA accumulation from a superinfecting virus. Synthesis of the E1A 289R protein by the first virus to infect reduced inhibition of transcription of the superinfecting virus, indicating that the E1A 289R protein was limiting for E1A-activated transcription. Infection with an E1A- virus, followed 6 h later by superinfection with a wild-type virus, led to preferential transcriptional activation of the E1A gene of the first virus, suggesting that a host transcription component(s) stably associated with the E1A promoter in the absence of E1A protein and that this complex was the substrate for transcriptional activation by E1A protein. The limiting host transcription component(s) bound to the E1A promoter to form a complex with a half-life greater than 24 h in the absence of E1A 289R protein, as demonstrated in a challenge assay with a large excess of superinfecting virus. In the presence of the E1A 289R protein, the E1A gene of the superinfecting virus was gradually activated with a reduction in E1A mRNA accumulation from the first virus. The kinetics of the activation suggest that this was due to an indirect effect rather than to destabilization of stable transcription complexes by the 289R protein.

E1A gene products stimulate in vitro transcription from the adenovirus early region 4 promoter by enhancing a stable preinitiation complex

A cell-free transcription system using nuclear extracts prepared from adenovirus type 5 (Ad5)-infected and mock-infected cells were utilized to study the E1A-mediated transactivation of transcription from the Ad5 early region 4 (E4) promoter. The transcription activity of Ad-infected cell extracts was several times higher than that of mock-infected cell extracts when the E4 wild-type (WT) promoter was used. The increased activity required expression of E1A proteins. However, the transcription activities of both cell extracts were not different when the mutant promoter containing only the E4 TATA box was used. The formation of a stable preinitiation complex at the E4 WT promoter was facilitated by expression of E1A, whereas it was not facilitated at the mutant promoter. The results suggested that the E1A proteins stimulated transcription from the E4 promoter by enhancing the formation of a stable preinitiation complex through the upstream elements, together with the TATA box.

TNF susceptibility-related gene expression

A series of BWL hybridoma lines has been generated by cell fusion of a TNF-resistant BW5147 cell line and a highly TNF-sensitive WR19L cell line, and has exhibited a wide variety of TNF susceptibility. A cDNA library, BWL47rp10, from a TNF-susceptible hybridoma line BWL47 has been screened by hybridization with a 32P-labeled subtraction cDNA probe from WR19L cells. Thirty-nine candidates for TNF susceptibility were cloned, and 20 clones larger than 1.0 kb have been examined so far. A cDNA clone, 10-2, hybridized to mRNA of 1.8 kb. It was expressed higher in highly TNF-sensitive cells, especially in BWL47, BWL40, and BWL57 cells. Thus, at least, the expression of the mRNA identified with cDNA 10-2 correlated well with TNF susceptibility in BWL cells, although its functional identity remains to be determined.

Activation in vitro of RNA polymerase II and III directed transcription by baculovirus produced E1A protein

The baculovirus expression system has been successfully used to overproduce a number of different protein products. In this report we describe the construction of a recombinant baculovirus containing the adenovirus E1A 13s cDNA sequence. Infection of insect cells with this virus results in the production of phosphorylated E1A protein. The phosphorylation pattern appears to be similar to the complex pattern associated with E1A protein synthesis in mammalian cells. Purified baculovirus generated E1A protein activated transcription of specific poIIII promoters both in microinjected Xenopus laevis oocytes and in HeLa cell in vitro transcription extracts. The protein also stimulates in vitro transcription of the poIIII transcribed VA1 gene.

Two distinct cellular proteins interact with the EIa-responsive element of an adenovirus early promoter

EIa-dependent transactivation of the adenovirus EIIa early (EIIaE) promoter is correlated with the activation of the cellular transcription factor E2F. In this study we identified a cellular protein, C alpha, that is distinct from E2F and that binds two sites in the EIIaE promoter, one of which overlaps with the proximal E2F binding site of the EIIaE promoter. The possible involvement of C alpha in the EIa responsiveness of this promoter is discussed.

E1a transactivation of human HSP70 gene promoter substitution mutants is independent of the composition of upstream and TATA elements

We have analyzed 41 deletion, linker scan, and substitution mutants of the human HSP70 gene promoter for activation by the adenovirus E1a region. No natural element of the HSP70 gene promoter was required for activation. To investigate specific interactions between E1a and transcription factors, a set of 24 promoters containing all possible combinations of eight different upstream or TATA motifs was investigated for E1a stimulation. E1a transactivated the promoter regardless of the particular TATA motif present. Furthermore, there was no dramatic correlation between any upstream motif and activation by E1a. These data suggest that E1a does not stimulate transcription via an interaction with any specific transcription factor but instead suggest that E1a interacts via the general transcription machinery.

E1a transactivation of human HSP70 gene promoter substitution mutants is independent of the composition of upstream and TATA elements

We have analyzed 41 deletion, linker scan, and substitution mutants of the human HSP70 gene promoter for activation by the adenovirus E1a region. No natural element of the HSP70 gene promoter was required for activation. To investigate specific interactions between E1a and transcription factors, a set of 24 promoters containing all possible combinations of eight different upstream or TATA motifs was investigated for E1a stimulation. E1a transactivated the promoter regardless of the particular TATA motif present. Furthermore, there was no dramatic correlation between any upstream motif and activation by E1a. These data suggest that E1a does not stimulate transcription via an interaction with any specific transcription factor but instead suggest that E1a interacts via the general transcription machinery.

Unusual levels of heat shock element-binding activity in embryonal carcinoma cells

In contrast to differentiated somatic cells, mouse embryonal carcinoma (EC) cell lines spontaneously express high levels of major members of the heat shock protein (HSP) family. In addition, some EC cell lines (noninducible) are not able to induce HSP gene transcription and HSP synthesis after a stress. However, after in vitro differentiation, constitutive HSP expression decreases and the differentiated derivatives become able to induce HSP gene transcription after a stress. These cells were tested by gel shift assays for the presence of an activity able to bind the heat shock element (HSE) before and after a stress. Control fibroblasts grown at 37 degrees C did not contain significant levels of HSE-binding activity, but heat shock dramatically increased the level of HSE-binding activity. In contrast to control fibroblasts, all EC cells contained significant levels of HSE-binding activity at 37 degrees C. In the inducible EC cell line F9, as in fibroblasts, heat shock strongly increased the level of HSE-binding activity. In the noninducible EC cells, however, HSE-binding activity markedly decreased upon heat shock. During in vitro differentiation of the noninducible cell line PCC7-S-1009, the constitutive HSE-binding activity found at 37 degrees C disappeared and heat induction of the HSE-binding activity appeared. Therefore, a good correlation exists between the high spontaneous expression of some members of the HSP family and the constitutive level of HSE-binding activity in EC cells at 37 degrees C. Heat induction of HSP gene transcription correlates with a strong increase in HSE-binding activity, whereas a deficiency in heat induction of HSP gene transcription is associated with a loss of HSE-binding activity upon heat shock.

Unusual levels of heat shock element-binding activity in embryonal carcinoma cells

In contrast to differentiated somatic cells, mouse embryonal carcinoma (EC) cell lines spontaneously express high levels of major members of the heat shock protein (HSP) family. In addition, some EC cell lines (noninducible) are not able to induce HSP gene transcription and HSP synthesis after a stress. However, after in vitro differentiation, constitutive HSP expression decreases and the differentiated derivatives become able to induce HSP gene transcription after a stress. These cells were tested by gel shift assays for the presence of an activity able to bind the heat shock element (HSE) before and after a stress. Control fibroblasts grown at 37 degrees C did not contain significant levels of HSE-binding activity, but heat shock dramatically increased the level of HSE-binding activity. In contrast to control fibroblasts, all EC cells contained significant levels of HSE-binding activity at 37 degrees C. In the inducible EC cell line F9, as in fibroblasts, heat shock strongly increased the level of HSE-binding activity. In the noninducible EC cells, however, HSE-binding activity markedly decreased upon heat shock. During in vitro differentiation of the noninducible cell line PCC7-S-1009, the constitutive HSE-binding activity found at 37 degrees C disappeared and heat induction of the HSE-binding activity appeared. Therefore, a good correlation exists between the high spontaneous expression of some members of the HSP family and the constitutive level of HSE-binding activity in EC cells at 37 degrees C. Heat induction of HSP gene transcription correlates with a strong increase in HSE-binding activity, whereas a deficiency in heat induction of HSP gene transcription is associated with a loss of HSE-binding activity upon heat shock.

The cellular transcription factor E2f requires viral E1A and E4 gene products for increased DNA-binding activity and functions to stimulate adenovirus E2A gene expression

Whereas a wide variety of cellular proteins interact with the cis-regulatory elements of the adenovirus E1A and E2A genes, only the DNA-binding activity of the cellular E2f factor is modulated by viral early-gene expression. An analysis of cellular E2f protein levels and adenovirus early-gene expression in a panel of independently cloned virus-transformed rodent cell lines and in virus-infected rodent cells has established that both the E1A 289-amino-acid (289R) protein and a yet-to-be-defined E4 gene product are required for maximal E2f DNA-binding activity. To distinguish between the multiple roles the E1A protein could serve in this process, the E2f DNA-binding activity was determined in a virus-transformed cell line which contains a conditional-lethal mutation affecting the 289R protein. Since E4 gene expression was not altered by the incubation conditions, the observation of reduced cellular E2f activity at the nonpermissive temperature suggests a direct role for the E1A 289R protein in E2f activation. When a virus containing a deletion in the E4 gene was introduced into cell lines which can complement the E4 gene defect, a correlation between high cellular E2f levels and increased rates of E2A gene transcription was observed. A time course analysis of the viral infection revealed that E2f functions catalytically to stimulate viral E2A gene transcription. These observations have led to several hypotheses concerning possible mechanisms by which elevated E2A gene expression, which leads to cytotoxicity, might be avoided in the transformed cell.

Transcriptionally active immediate-early protein of pseudorabies virus binds to specific sites on class II gene promoters

In the presence of partially purified pseudorabies virus immediate-early protein, multiple sites of DNase I protection were observed on the adenovirus major late and human hsp 70 promoters. Southwestern (DNA-protein blot) analysis demonstrated that the immediate-early protein bound directly to the sequences contained in these sites. These sequences share only limited homology, differ in their affinities for the immediate-early protein, and are located at different positions on these two promoters. In addition, the site-specific binding of a temperature-sensitive immediate-early protein was eliminated by the same heat treatment which eliminates its transcriptional activating function, whereas the binding of the wild-type protein was unaffected by heat treatment. Thus, site-specific binding requires a functionally active immediate-early protein. Furthermore, immediate-early-protein-dependent in vitro transcription from the major late promoter was preferentially inhibited by oligonucleotides which are homologous to the high-affinity binding sites on the major late or hsp 70 promoters. These observations suggest that transcriptional stimulation by the immediate-early protein involves binding to cis-acting elements.

Genetic dissection of the transactivating domain of the E1a 289R protein of adenovirus type 2

A series of linker-scanning, deletion, and frameshift mutations were made in the pm975 variant of the adenovirus type 2 E1a gene, which expresses only the larger of the two major E1a proteins. Most of these were within the 46-amino-acid segment unique to the larger E1a protein product (the 289R protein), which confers on it the ability to activate in trans the expression of other genes. The mutations were recombined into virus and assayed by in vitro transcription in nuclei isolated from infected cells for their ability to activate the transcription of other viral early genes and of the endogenous hsp70 gene. Mutant E1a proteins from which the 289R-unique segment was removed by deletion or truncation did not completely lose the ability to transactivate by comparison with a virus which makes no E1a at all, indicating that sequences outside this domain are active in the positive regulation of transcription. The E1a mutations tested fell into several classes: those that increased transactivation of virtually all genes, those that severely depressed transactivation of all genes, and those that depressed transactivation only moderately. Each mutation had similar effects on the expression of all transcription units tested, indicating a common process in their transactivation. However, some mutants in the third category decreased transactivation of some induced genes more severely than of others. Such gene-specific defects suggest the existence of subclasses of E1a-responsive transcription units, consistent with the involvement of diverse proteins in the transactivation of different genes. Two specific structural components of the transactivating domain, a putative metal-binding element and a region with high potential for beta-sheet formation at its carboxy-terminus, appear to be important to the transactivation function.

Phosphorylation of serine residue 89 of human adenovirus E1A proteins is responsible for their characteristic electrophoretic mobility shifts, and its mutation affects biological function

The shift in mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis that is characteristic of the adenovirus E1A proteins is the result of posttranslational modification. In the present study, we demonstrate that phosphorylation of bacterially produced E1A in higher cell extracts occurs on serine and is responsible for the mobility shift. E1A protein expressed in Saccharomyces cerevisiae also undergoes the mobility shift due to serine phosphorylation. Site-directed mutagenesis was used to identify the serine residue responsible for the mobility shift. Six serine residues were altered to glycine within E1A. Substitution at serine residue 89 was shown to selectively prevent the mobility shift of both the 289R and 243R E1A proteins. We conclude that phosphorylation at serine 89 is the specific modification responsible for the mobility shift of E1A. Moreover, we demonstrate that the Ser-89-to-Gly mutation has no effect on trans activation or complementation of an E1A-deficient adenovirus. In contrast, the mutant protein does significantly reduce both the repression and transformation efficiency of E1A. The five other Ser-to-Gly mutation were also examined for functional effects. None affected trans activation, whereas repression and transformation functions were affected. One mutant affected transformation without affecting repression, suggesting that these functions are to some degree also separable. The relevance of phosphorylation to structure and activity of E1A and other nuclear oncogene proteins is discussed.

Cis- and trans-acting factors for transcription of the adenovirus 12 E1A gene

Cis- and trans-acting factors were analyzed for transcription of the adenovirus 12 E1A gene possessing two sites for transcription initiation. These sites are located at nucleotide positions 306 and 445 with respect to the left end of the viral genome as position 1. The template activity of DNAs with various deletions at the 5'-upstream region of the E1A gene was examined in a cell-free system using a nuclear extract of Ehrlich ascites tumor cells. A DNA region specifically stimulating transcription initiated at the site distal to the E1A coding sequence was found located between positions 1 and 166. No DNA sequence affecting transcription from a proximal start-site appeared to be present in the region between positions 1 and 378. DNaseI-footprinting indicated that factors present in the extract bind to two distinct DNA segments, both of which are located within a region stimulating distal transcription. Two footprints were observed, one between positions 19 and 55 and the other between 77 and 94. The former footprint was inhibited by synthetic oligonucleotides containing a sequence recognized by nuclear factor I and the latter contained a sequence similar to one present in the B-enhancer of polyoma virus. Competition of in vitro transcription with synthetic oligonucleotides indicated (a) nuclear factor(s) bound to the region between positions 19 and 55 to be responsible for stimulating distal transcription of the adenovirus 12 E1A gene.

Transcriptional regulation by the immediate early protein of pseudorabies virus during in vitro nucleosome assembly

An in vivo transcriptional activator, the immediate early protein (IE) of pseudorabies virus, potentiates the activity of the major late promoter in a reconstituted chromatin assembly system where the assembly of preinitiation complexes is in competition with the assembly of promoter sequences within nucleosomes. IE function requires the simultaneous action of TFIID and results in the formation of stable preinitiation complexes within nucleosome-assembled templates. IE is unable to reverse nucleosome-mediated repression, once established, or to further increase the activity of previously activated templates. These results indicate that IE stimulates TFIID binding to promoter sequences, effectively competing with nucleosomes, during chromatin reconstitution. The specific implications for IE function in vivo and the general implications for cellular gene regulation are discussed.

Distinctive charge configurations in proteins of the Epstein-Barr virus and possible functions

The protein products of several open reading frames (ORFs) of the Epstein-Barr virus (EBV) are remarkable in their distribution of charged residues. The nuclear antigen proteins EBNA1-EBNA4 of the EBV latent state contain separate significant clusters of charge of each sign. They (excepting EBNA4) also feature distinctive periodic charge patterns [e.g., (+, O)8, (O, -, -)7] and significant tandem repeats. None of the other ORFs (about 80) of the genome possess the conjunction of these properties. Only the protein encoded from BMLF1, the first immediate early transactivator protein, contains significant multiple charge clusters and periodic charge patterns. All proteins that contain significant repeats also contain at least one significant charge cluster of a single sign. These include EBNA5 and LYDMA produced during latency and BZLF1, whose expression terminates latency and initiates productive growth. It is reasonable to conclude that these aggregate significant charge configurations and repeats are important functionally for the latent existence and for the initiation of the lytic cycle and may be characteristic of these conditions. We discuss how large multimeric protein structures bound together by clusters of unlike charge may provide a mechanism for regulation of the expression of these proteins.

The 289-amino acid E1A protein of adenovirus binds zinc in a region that is important for trans-activation

The E1A gene of adenovirus type 5 encodes two major proteins of 289 and 243 amino acid residues, which are identical except that the larger protein has an internal stretch of 46 amino acids required for efficient trans-activation of early viral promoters. This domain contains a consensus zinc finger motif (Cys-Xaa2-Cys-Xaa13-Cys-Xaa2-Cys) in which the cysteine residues serve as postulated ligands. Atomic absorption spectrophotometry applied to bacterially expressed E1A proteins revealed that the 289-amino acid protein binds one zinc ion, whereas the 243-amino acid protein binds no zinc. Replacing individual cysteine residues of the finger with other amino acids destroyed the trans-activating ability of the 289-amino acid protein, even when structurally or functionally conserved amino acids were substituted. These results strongly suggest that the zinc finger of the 46-amino acid domain is intimately linked to the ability of the large E1A protein to stimulate transcription of E1A-inducible promoters. Furthermore, zinc binding to one of the mutant finger proteins suggests either that only a precise finger structure formed by the tetrahedral coordination of zinc to the four consensus ligands is required for trans-activation or, possibly, that one of several neighboring histidine residues in various combinations with three of the consensus cysteine residues normally coordinates zinc. How the zinc finger in E1A might interact with DNA or protein to bring about trans-activation is discussed.

An adenovirus E1A protein domain activates transcription in vivo and in vitro in the absence of protein synthesis

We have shown previously that a synthetic peptide of 49 amino acids, encoding mainly adenovirus E1A protein domain 3 (PD3), functions as an autonomous transcriptional activator. Here we provide two lines of evidence showing that E1A transactivation does not require the induction of cellular protein synthesis. First, PD3 rapidly transactivates E1A-inducible early viral genes in the presence of inhibitors of protein synthesis, as demonstrated by microinjection-in situ hybridization experiments. Second, PD3 greatly stimulates transcription of E1A-inducible genes in vitro. Mutant PD3 peptides with single amino acid substitutions in conserved cysteine residues are defective in transactivation both in vivo and in vitro. Our findings provide compelling evidence that protein synthesis is not required for E1A transactivation, and support a model in which E1A modifies the activity of a preexisting cellular protein(s) involved in the regulation of transcription.

Activation of transcription factor IIIC by the adenovirus E1A protein

The factor(s) responsible for the adenovirus E1A-stimulated transcription of RNA polymerase III genes was localized previously in a chromatographic fraction containing transcription factor IIIC (TFIIIC). In further studies, two distinct forms of TFIIIC, which were chromatographically separable, generated VA gene-protein complexes that were distinguished by gel shift assays. The form of TFIIIC that generated the more slowly migrating promoter complex had greater transcriptional activity in vitro, associated more rapidly with the promoter, and formed a more salt-resistant complex. Greater amounts of this more active form of TFIIIC resulted from either E1A expression during infection or growth of the cells in a higher concentration of serum, whereas template commitment assays indicated that overall TFIIIC concentrations remained unchanged during viral infection. The in vitro interconversion of the two forms of TFIIIC by phosphatase treatment suggests that transcriptional activation of RNA polymerase III genes can be mediated by phosphorylation of TFIIIC.

The pseudorabies immediate early protein stimulates in vitro transcription by facilitating TFIID: promoter interactions

The pseudorabies virus immediate early (IE) protein, partially purified from infected HeLa cells, stimulated transcription initiation by RNA polymerase II and associated factors in HeLa nuclear extracts. This stimulation was maximal at low template concentrations, where the basal level of transcription was also low. In an analysis of the limitations on transcription under these conditions, it was found that transcription could be increased drastically not only by IE addition but also by (1) the addition of nonpromoter-containing DNA, which titrated nonspecific DNA-binding proteins in the crude nuclear extract, and (2) preincubation of the template with either the nuclear extract (in the absence of Mg2+) or with the TATA box-binding factor, TFIID. These results suggest that in the absence of IE, nonspecific DNA-binding proteins competed with TFIID for binding to the promoter, thus making TFIID: promoter interactions limiting for transcription. The stimulation of transcription effected by IE was essentially the same as that observed following preassociation of TFIID with the template or by titration of nonspecific DNA-binding proteins. Moreover, the presence of IE under the latter conditions did not stimulate transcription further. These observations strongly suggest that all of these manipulations affected the same limiting step and, thus, that IE accentuated the rate or extent of formation of a preinitiation complex involving the TATA factor, rather than subsequent initiation or elongation steps.

Purification and functional characterization of a cellular transcription factor that binds to an enhancer element within the adenovirus early EIIa promoter

The adenovirus EIa-inducible early EIIa (EIIaE) promoter is comprised of several sequence elements essential for constitutive and induced expression. We report here the purification of the host-cell factor that interacts with the major upstream element of this promoter, extending between positions -90 and -70 with respect to the main EIIaE cap site and exhibiting enhancer properties. The purified factor, which corresponds to a 40- to 43-kDa polypeptide, specifically binds to its recognition site and stimulates EIIaE promoter activity when added to an in vitro transcription system, reconstituted from purified factors and RNA polymerase. The implication of this factor in the control of the other adenovirus early genes is discussed.

Trans-acting protein factors and the regulation of eukaryotic transcription: lessons from studies on DNA tumor viruses

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Identification of factors that interact with the E1A-inducible adenovirus E3 promoter

We have investigated the E1A-inducible E3 promoter of adenovirus type 5 with respect to its ability to bind specific nuclear proteins. Four distinct nucleoprotein-binding sites were detected, located between positions-7 to -33, -44 to -68, -81 to -103, and -154 to -183, relative to the E3 cap site. These sites contain sequences previously shown to be functionally important for efficient E3 transcription. No major qualitative or quantitative differences were found in the binding pattern between nucleoprotein extracts prepared from uninfected or adenovirus-infected HeLa cells. Competition experiments suggest that the factors binding to the -154 to -183 and -81 to -103 sites are the previously identified nucleoproteins, NF1 and AP1, respectively. The factor binding to the -44 to -68 site, which we term ATF, also interacts with other E1A-inducible promoters and is very similar and probably identical to the factor that binds to the cAMP-responsive element of somatostatin. We have purified this factor, which is a protein of 43 kD in size.