Stimulation of the adenovirus E2 promoter by simian virus 40 T antigen or E1A occurs by different mechanisms

Effects of mutation of the CREB binding site of the somatostatin promoter on cyclic AMP responsiveness in CV-1 cells

The transcription factors CREB (cAMP response element binding protein) and ATF (activating transcription factor) recognize DNA containing the consensus sequence TGACGTCA. We compared the neuropeptide somatostatin promoter, which binds CREB and is activated by cAMP, to the adenovirus E2A promoter, which binds ATF but is not activated by cAMP, to determine which specific nucleotides within a CREB/ATF recognition sequence confer cAMP responsiveness. Several mutant somatostatin promoters were generated containing part of all of the E2A ATF binding site. Some of the hybrid CREB/ATF binding sites competed for factor binding to a wild-type somatostatin promoter probe. However, only the wild-type CREB binding site promoter could confer cAMP activation on a linked CAT plasmid. Furthermore, this wild-type CREB binding site could confer cAMP activation on the CAT plasmid only if it was adjacent to a wild-type somatostatin TATA box and cap site. These results suggest that slight deviation from a wild-type CREB recognition sequence might be tolerated by factor(s) binding to cAMP response element-like sequences. However, transcription activation may require a particular CREB recognition sequence, as well as additional promoter elements that bind proteins that interact with CREB.

Co-infection with human polyomavirus BK enhances gene expression and replication of human adenovirus

Immunocompromised patients are susceptible to multiple viral infections. Relevant interactions between co-infecting viruses might result from viral regulatory genes which trans-activate or repress the expression of host cell genes as well as the genes of any co-infecting virus. The aim of the current study was to show that the replication of human adenovirus 5 is enhanced by co-infection with BK polyomavirus and is associated with increased expression of proteins including early region 4 open reading frame 1 and both the large tumor antigen and small tumor antigen. Clinical samples of whole blood and urine from 156 hematopoietic stem cell transplant recipients were tested. We also inoculated adenocarcinomic human alveolar basal epithelial cells with both human adenovirus 5 and BK polyomavirus to evaluate if co-infection of viruses affected their replication. Data showed that adenovirus load was significantly higher in the plasma (mean 7.5 x 10³ ± 8.5 x 10² copies/ml) and urine (mean 1.9 x 10³ ± 8.0 x 10² copies/ml) of samples from patients with co-infections, in comparison to samples from patients with isolated adenovirus infection. In vitro co-infection led to an increased (8.6 times) expression of the adenovirus early region 4 open reading frame gene 48 hours post-inoculation. The expression of the early region 4 open reading frame gene positively correlated with the expression of BK polyomavirus large tumor antigen (r = 0.90, p < 0.0001) and small tumor antigen (r = 0.83, p < 0.001) genes. The enhanced expression of the early region 4 open reading frame gene due to co-infection with BK polyomavirus was associated with enhanced adenovirus, but not BK polyomavirus, replication. The current study provides evidence that co-infection of adenovirus and BK polyomavirus contributes to enhanced adenovirus replication. Data obtained from this study may have significant importance in the clinical setting.

The Nuclear Matrix Protein, NRP/B, Acts as a Transcriptional Repressor of E2F-mediated Transcriptional Activity

Background:

NRP/B, a family member of the BTB/Kelch repeat proteins, is implicated in neuronal and cancer development, as well as the regulation of oxidative stress responses in breast and brain cancer. Our previous studies indicate that the NRP/B-BTB/POZ domain is involved in the dimerization of NRP/B and in a complex formation with the tumor suppressor, retinoblastoma protein. Although much evidence supports the potential role of NRP/B as a tumor suppressor, the molecular mechanisms of NRP/B action on E2F transcription factors have not been elucidated.

Methods:

Three-dimensional modeling of NRP/B was used to generate point mutations in the BTB/Kelch domains. Tet-on inducible NRP/B expression was established. The NRP/B deficient breast cancer cell line, MDA-MB-231, was generated using lentiviral shNRP/B to evaluate the effect of NRP/B on cell proliferation, invasion and migration. Immunoprecipitation was performed to verify the interaction of NRP/B with E2F and histone deacetylase (HDAC-1), and the expression level of NRP/B protein was analyzed by Western blot analysis. Changes in cell cycle were determined by flow cytometry. Transcriptional activities of E2F transcription factors were measured by chloramphenicol acetyltransferase (CAT) activity.

Results:

Ectopic overexpression of NRP/B demonstrated that the NRP/B-BTB/POZ domain plays a critical role in E2F-mediated transcriptional activity. Point mutations within the BTB/POZ domain restored E2-promoter activity inhibited by NRP/B. Loss of NRP/B enhanced the proliferation and migration of breast cancer cells. Endogenous NRP/B interacted with E2F and HDAC1. Treatement with an HDAC inhibitor, trichostatin A (TSA), abolished the NRP/B-mediated suppression of E2-promoter activity. Gain or loss of NRP/B in HeLa cells confirmed the transcriptional repressive capability of NRP/B on the E2F target genes, Cyclin E and HsORC (Homo sapiens Origin Recognition Complex).

Conclusions:

The present study shows that NRP/B acts as a transcriptional repressor by interacting with the co-repressors, HDAC1, providing new insight into the molecular mechanisms of NRP/B on tumor suppression.

PCR diagnostics and monitoring of adenoviral infections in hematopoietic stem cell transplantation recipients

After stem cell transplantation, human patients are prone to life-threatening opportunistic infections with a plethora of microorganisms. We report a retrospective study on 116 patients (98 children, 18 adults) who were transplanted in a pediatric bone marrow transplantation unit. Blood, urine and stool samples were collected and monitored for adenovirus (AdV) DNA using polymerase chain reaction (PCR) and real-time PCR (RT-PCR) on a regular basis. AdV DNA was detected in 52 (44.8%) patients, with mortality reaching 19% in this subgroup. Variables associated with adenovirus infection were transplantations from matched unrelated donors and older age of the recipient. An increased seasonal occurrence of adenoviral infections was observed in autumn and winter. Analysis of immune reconstitution showed a higher incidence of AdV infections during periods of low T-lymphocyte count. This study also showed a strong interaction between co-infections of AdV and BK polyomavirus in patients undergoing hematopoietic stem cell transplantations.

The human polyomavirus BK T antigen induces gene expression in human cytomegalovirus

Co-infections or co-habitations of cells by two or more viruses may occur in the human organism. Human cytomegalovirus (HCMV) and the human polyomavirus BK (BKV) have common host cells and may both establish lifelong latency/persistence following primary infection. Both viruses may become reactivated by immunosuppression or other conditions which upset host-virus balance, and they encode gene products with the inherent potential of acting as heterologous transacting factors for expression of cellular or viral genes. It has been shown that HCMV induces gene expression and replication of primate polyomaviruses. We now demonstrate that BKV is able to enhance the expression of HCMV immediate early (IE1 and 2) as well as the early (E) protein pp65 during double infections in semi-permissive cells. By transfection experiments it was established that the phenomenon is due to heterologous transcriptional transactivation of the HCMV major IE promoter (MIEP) by the BKV large T antigen, without contribution from the small t antigen.

Abrogation of p53 function affects gadd gene responses to DNA base-damaging agents and starvation

The tumor suppressor p53 is required for induction of its downstream effector genes such as GADD45 and CIP1/WAF1 by ionizing radiation (IR). This response is probably mediated through defined p53 binding sites located in the promoter of CIP1/WAF1 and in the third intron of GADD45. In contrast, the gadd gene stress response to base-damaging agents, such as methylmethane sulfonate (MMS) or UV radiation, or medium depletion (starvation) occurs in all mammalian cells examined to date regardless of p53 status for both GADD45 and also GADD153, which is not IR-responsive in many lines with functional p53. These agents strongly induce the p53 protein and raise the possibility that, although p53 is not required for the typical "gadd" response to these agents, p53 may contribute to these non-IR stress responses. This possibility was confirmed by the finding that disruption of p53 function by transfection with dominant-negative vectors expressing HPV E6, mutant p53, or SV40 T Ag reduced the induction of GADD45 and GADD153 as measured by increases in mRNA and protein levels in human lines with wild-type p53. Similarly, induction of these genes by MMS or UV radiation was consistently stronger in the parental mouse embryo fibroblasts compared to cells derived from mice where both p53 alleles had been deleted. Similar qualitative responses were also seen for CIP1/WAF1. In agreement with reduced induction of p53-regulated genes, the G1 checkpoint activated by MMS or UV radiation was markedly abrogated in p53-wt human MCF-7 breast carcinoma cells by E6 expression. Interestingly, induction of reporter constructs driven by the GADD45 or GADD153 promoters was substantially reduced in human cells transfected with mutant p53 or E6 expression vectors or in cells lacking p53 following treatment with MMS, UV radiation, or starvation. Because neither promoter is inducible by IR, and neither contains a strong p53 binding site, these results indicate that p53 has a synergistic or cooperative role in these non-IR stress responses for both GADD45 and GADD153, and that this role is not mediated through identifiable p53-binding sites.

Expression of the gene encoding glycogen phosphorylase is elevated in diabetic rat skeletal muscle and is regulated by insulin and cyclic AMP

Glycogen phosphorylase regulates the breakdown of glycogen into glucose, but as previous studies have demonstrated, the control of glycogen metabolism becomes deregulated in diabetes mellitus. Messenger RNA levels encoding several different proteins are altered in skeletal muscle biopsies of patients with insulin-dependent and non-insulin-dependent diabetes. The possible alteration of expression of the gene encoding the skeletal muscle isoform of glycogen phosphorylase during diabetes has not previously been investigated. We examined the effect of streptozotocin-induced diabetes and insulin treatment on glycogen phosphorylase mRNA in rat skeletal muscle; glycogen phosphorylase mRNA levels were elevated in diabetic rat muscle tissue, but were partially suppressed in diabetic rat muscle following insulin treatment. To distinguish between the effects of insulin and counter-regulatory hormones on glycogen phosphorylase mRNA levels, we employed differentiating rat L6 myoblasts in culture. Insulin stimulated the accumulation of glycogen phosphorylase mRNA as determined by Northern blot analysis. Moreover, insulin and dibutyryl cAMP stimulated expression of a transiently transfected chloramphenicol acetyl transferase reporter gene under the control of the muscle glycogen phosphorylase promoter in differentiating myotubes in culture, suggesting that the effects of insulin and counter-regulatory hormones on glycogen phosphorylase mRNA are at the level of transcription. These results suggest that insulin and epinephrine may participate in the induction of the glycogen phosphorylase gene during myogenesis; moreover, activation of this gene in muscle tissue may be a contributing factor in impaired glycogen storage during uncontrolled diabetes.

Interaction between T antigen and TEA domain of the factor TEF-1 derepresses simian virus 40 late promoter in vitro: identification of T-antigen domains important for transcription control

The large tumor antigen (TAg) of simian virus 40 regulates transcription of the viral genes. The early promoter is repressed when TAg binds to the origin and DNA replication begins, whereas the late promoter is activated by TAg through both replication-dependent and -independent mechanisms. Previously it was shown that activation is diminished when a site in the viral enhancer to which the factor TEF-1 binds is disrupted. We show here that the NH2-terminal region of TAg binds to the TEA domain of TEF-1, a DNA binding domain also found in the Drosophila scalloped and the Saccharomyces cerevisiae TEC1 proteins. The interaction inhibits DNA binding by TEF-1 and activates transcription in vitro from a subset of naturally occurring late start sites. These sites are also activated by mutations in the DNA motifs to which TEF-1 binds. Therefore, TEF-1 appears to function as a repressor of late transcription, and its involvement in the early-to-late shift in viral transcription is discussed. The mutation of Ser-189 in TAg, which reduces transformation efficiency in certain assays, disrupts the interaction with TEF-1. Thus, TEF-1 might also regulate genes involved in growth control.

E1A promotes association between p300 and pRB in multimeric complexes required for normal biological activity

The oncogenes of the small DNA tumor viruses encode transforming proteins with multiple domains that influence the cell cycle and aspects of the transformed phenotype. Like other gene products of this type, the adenovirus E1A proteins influence the cell by binding to specific cell growth control proteins. These include members of the retinoblastoma gene product (pRB) family, which are bound by the E1A region 2-specific site, and p300, which is bound at the E1A amino terminus. Binding at these two sites is largely independent, and discrete transcription-regulating functions remain intact in E1A products when only one or the other binding site is functional. In this report, immunoprecipitation with p300 antibodies reveals the presence of the pRB family proteins in p300 complexes when E1A is expressed in host cells, indicating that E1A can mediate physical contact between p300 and the pRB-related proteins. The ability of E1A to induce proliferation efficiently in quiescent primary cells correlates closely with the ability to bind p300 and individual members of the pRB family simultaneously in multimeric complexes, even though the E1A active sites can bind their target proteins efficiently when separated on different molecules. Conservation of a spacer region between the two binding sites that is required for simultaneous binding and efficient induction of proliferation supports the concept that the E1A protein structure has evolved to facilitate simultaneous binding. These results indicate that the E1A proteins are designed not merely to sequester these cellular products, but also to bring them into proximal association with each other in biologically significant complexes.

Transcriptional activation of the human T-lymphotropic virus type I long terminal repeat by functional interaction of Tax1 and Ets1

Transcription regulation of the oncogenic retrovirus human T-lymphotropic virus type I (HTLV-I) involves the composite activity of both viral and cellular transcription factors. The HTLV-I transforming protein, Tax1, modulates the activity of several cellular transcription factors, upregulating the level of viral gene expression. In addition, cellular transcription factors, such as Ets1, independently bind to the viral long terminal repeat in a sequence-specific manner and activate transcription. It was of interest to analyze the possible interaction of Tax1 and Ets1 in viral gene regulation. We now report that Tax1 and Ets1 increase expression from the HTLV-I promoter in a cooperative manner. The level of expression was increased 5- to 10-fold above the combined individual effect of Tax1 and Ets1. S1 nuclease analysis demonstrated that the cooperative effect was due to an increase in the levels of steady-state RNA. The functional interaction between Tax1 and Ets1 required the presence of the Tax1-responsive 21-bp repeat element TRE-1 and the Ets1-responsive element ERR-1. These results suggested the possible interaction of Ets1 with transcriptional regulatory proteins that bind to the 21-bp repeats. This interaction is demonstrated by decreased electrophoretic mobility of specific 21-bp repeat gel shift complexes in the presence of Ets1. Furthermore, interaction of Ets1 with the 21-bp repeat-binding proteins enhances the relative efficiency of binding to the DNA. This cooperative interaction between Ets1 and proteins which bind to the Tax1-responsive 21-bp repeats suggests a possible role for Ets1 in the regulation of viral gene expression.

Multiple, distinct trans-activation functions are encoded by the simian virus 40 large T and small t antigens, only some of which require the 82-residue amino-terminal common domain

Simian virus 40 (SV40) small t and large T antigens can each trans activate the adenovirus (Ad) E2A and the Ad VA-I promoters. The first 82 amino acids of large T and small t are identical. However, this large T-small t common domain between residues 1 and 82 does not trans activate, suggesting that large T and small t each encode separate trans-activation functions. To determine whether the large T or small t unique domains, which are required for trans activation of the E2A promoter, are sufficient for this activity, we have employed expression plasmids separately encoding the common and unique domains of large T and small t. Cotransfection of a large T unique domain expression plasmid efficiently trans activated the E2A promoter. Optimal trans activation by large T required the motif that binds cellular proteins such as the retinoblastoma gene product, which is located in the large T unique domain, and additional large T structures outside this motif. In contrast, the small t unique domain did not trans activate the E2A promoter. Experiments utilizing E2A promoter mutants containing only the ATF- or EIIF-binding sites demonstrated that trans activation by small t involves only the EIIF transcription factor and that this function requires both the common (residues 1 to 82) and the small t unique domains expressed as a colinear protein. trans activation by large T, in contrast, involves at least three mechanisms. There appear to be at least two mechanisms that involve the EIIF transcription factor, at least one of which does not require the common domain (residues 1 to 82) and one mechanism that involves the ATF factor and does require both the common and the large T unique domains.

DNA tumor virus transforming proteins and the cell cycle

Studies using the transforming proteins of the small DNA tumor viruses point to the role of the E2F cellular transcription factor in regulating cell cycle specific gene expression. The evidence derived suggests that E2F is controlled by the retinoblastoma gene product and related proteins, including their associated cyclins. Studies using DNA tumor virus products further suggest the existence of additional pathways of cell-cycle activation.

Effect of low extracellular Ca2+ on growth, spreading area, cytoplasmic Ca2+ concentration, and intracellular pH in normal and transformed human fibroblasts

The transformation of certain cells reduces the requirement of extracellular Ca2+ for growth. The SV-40 transformed human lung fibroblasts, WI-38 VA13, require less Ca2+ than normal WI-38 cells. Spreading area of the normal cells decreases when cultured in 10 microM Ca2+ medium. Intracellular calcium concentration ([Ca2+]i) of the normal and transformed cells cultured in 10 microM and 2 mM Ca2+ media was measured by the fluorescence microscope technique using fura-2 as a probe. The [Ca2+]i is measured in the resting state and during mobilization by serum or bradykinin stimulation. The lowering of extracellular calcium concentration results in a decrease in the resting state [Ca2+]i of both normal and transformed cells. Although the total decrease in [Ca2+]i is the same for both cells, the rate of decrease is much faster in normal cells than in transformed cells. Low extracellular Ca2+ reduces the number of cells responsive to the serum or bradykinin stimulation and decreases the peak [Ca2+]i value in both cells. In addition, we investigated, using BCECF as a fluorescent probe, the intracellular pH (pHi) of normal and transformed cells maintained at low and normal Ca2+. The low Ca2+ condition makes pHi acidic in normal cells but not in transformed cells. The acidification of the normal cell is accompanied by a decrease in the spreading area of the cells. The decrease of the cell attachment, followed by the reduced spreading area, induces the acidic pHi. These results suggest that the reduced Ca2+ requirement of transformed cells for growth is related to the mechanism of pHi regulation rather than Ca2+ homeostasis and, possibly, to the anchorage-independent growth, which is a unique feature of transformed cells.

SV40 large T antigen trans-activates the long terminal repeats of a large family of human endogenous retrovirus-like sequences

The Simian Virus 40 (SV40) large T antigen (T) is required for the initiation of viral replication, the autoregulation of early gene expression, and the activation of late gene expression in productively infected cells. In addition to these roles, T has been implicated in the transcriptional activation of a variety of viral and cellular promoters. We have used the chloramphenicol acetyltransferase (CAT) reporter gene system to study the effect of T on the long terminal repeats (LTRs) of a large family of human endogenous retrovirus-like sequences, RTVL-H. Here we show that T can activate expression from certain RTVL-H LTRs 5- to 30-fold. Competition experiments in which an excess of plasmid containing only an RTVL-H LTR was cotransfected with an LTR-CAT reporter gene construct confirmed that this effect is specific for RTVL-H sequences. Restriction enzyme analysis using methylation-sensitive enzymes has shown that this activation is not due to plasmid replication. We have also observed this trans-activation effect in two CV-1 cells lines containing stably integrated LTR-CAT constructs. These results demonstrate that a known transforming protein can alter the transcriptional capabilities of RTVL-H LTRs. As there are approximately 3000 related LTRs in the genomes of humans and other primates, these findings suggest that a large number of these promoters and their associated transcripts may be transcriptionally stimulated by this and other oncogens.

Analysis of trans activation by human papillomavirus type 16 E7 and adenovirus 12S E1A suggests a common mechanism

The human papillomavirus E7 gene product is an oncoprotein with properties similar to those of the adenovirus E1A proteins. The human papillomavirus E7 proteins possess substantial amino acid sequence similarity to portions of conserved regions 1 and 2 of E1A, and the human papillomavirus type 16 E7 protein trans-activates the adenovirus E2 early promoter. Analysis of point mutations in the E2 promoter indicated that the E2F recognition sites were critical to E7 stimulation. In contrast to the activation of the E2 promoter, E7 could not trans-activate various other E1A-inducible promoters. Although the promoter specificity for E7 differs from that of 13S E1A trans activation, it is very similar to activation by the E1A 12S product. Moreover, analysis of the E7 protein has suggested that amino acid sequences critical for trans activation include those shared with E1A within conserved region 2. Biochemical studies demonstrate that the E7 protein, like the 12S E1A product, can alter the interaction of cellular factors with the E2F transcription factor. We therefore conclude that E7 trans activation is functionally related to that mediated by the 12S E1A product.

Construction and uses of cell lines containing integrated adenovirus E2 promoters

The adenovirus E1a gene encodes polypeptides which regulate the expression of adenovirus early genes as well as a variety of cellular genes. Although it is likely that the E1a encoded polypeptides regulate the expression of these genes by interaction with a variety of cellular transcription factors, the precise mechanism by which this occurs is currently unknown. This report describes the development of cell lines which contain integrated copies of the E2 promoter driving the expression of the Tn5 neo gene or the Escherichia coli beta-galactosidase gene. In each case phenotypic changes concurrent with expression of the E1a 289 amino acid polypeptide are demonstrated. The use of these cell lines to detect rare events in the activation of the E2 promoter is demonstrated in transfection experiments. These cell lines are also used to study the effects of c-myc expression on integrated E2 promoters.

T-antigen is not bound to the replication origin of the simian virus 40 late transcription complex

Simian virus 40 tumor antigen (T-antigen) plays a central role in determining which gene is transcribed from viral DNA late in infection. Results from several studies have led to a model in which the binding of T-antigen to the viral origin of replication results in repression of transcription from the stronger early gene promoter and stimulation of transcription from the late gene promoter. We have tested this model by determining directly the occupancy of the T-antigen binding site in the origin of replication of the late transcription complex. Thus, viral transcription complexes were digested with BglI, a restriction enzyme that cuts in the viral replication origin. The enzyme cleaved 78(+/- 12)% of the late transcription complexes. Control experiments demonstrated that cleavage is blocked when T-antigen is bound to the origin site, that exogenously added T-antigen can bind to the site in the transcription complex, and that T-antigen is not released during isolation of the complex. These results indicate that most of the late transcription complexes do not have T-antigen bound to the origin site, and are therefore inconsistent with models that require this site to be occupied by T-antigen to maintain proper regulation of gene transcription late in infection.

Dissociation of Rb-binding and anchorage-independent growth from immortalization and tumorigenicity using SV40 mutants producing N-terminally truncated large T antigens

The large T antigen of SV40 is both necessary and sufficient for conversion of primary mouse cells to cells with fully transformed phenotype. In this investigation, the influence of the N-terminal portion of T antigen on individual transformed cell characteristics was probed by using mutants bearing deletions in the 5'T antigen coding sequence. Specifically, DNA constructs expected to produce T antigens missing the first 109, 127, 150, or 176 amino acids or internal amino acid segments between 117 and 250 were tested for the ability to immortalize C57Bl/6 mouse embryo fibroblasts. The transformed cell properties displayed by clonally derived cell lines were then examined. The results indicated that neither the first 127 amino acids nor amino acids 127-250 of T antigen were necessary for efficient immortalization of primary cells or for their tumorigenicity. Functions mapped within these regions, including binding of the retinoblastoma susceptibility gene product (Rb) and transactivation of heterologous promoters, therefore, were not required to confer either of these growth properties. In addition the results showed that anchorage-independent growth was separable genetically from tumorigenicity and that removal of amino acids within the first 250 residues of T antigen compromised other transformed cell growth properties.

trans-activation of RNA polymerase II and III promoters by SV40 small t antigen

A biochemical role for SV40 small t antigen (t) in the viral infectious cycle that would explain the strong conservation of t structure among papovaviruses and its role as a helper of SV40 large T antigen function in the viral transforming process is not understood. Here, we report an intracellular biochemical function of the protein--the capacity to trans-activate selected RNA polymerase II and III-requiring promoters. Since t has failed in the past to bind to DNA and did not stimulate all polymerase II-requiring promoters tested, it likely trans-activates, at least in part, by modifying the activity of selected transcription factors.

A transcriptional repressor encoded by BPV-1 shares a common carboxy-terminal domain with the E2 transactivator

A negative-acting transcriptional regulatory factor encoded by bovine papillomavirus type 1 (BPV-1) was identified. This factor inhibits BPV-1-mediated transformation of mouse C127 cells; inhibition is BPV-1-specific and occurs only when the BPV-1 transforming genes are regulated by authentic transcriptional control elements. Plasmids expressing the inhibition function also repress E2 transactivation of the BPV-1 E2-dependent enhancer, and this repression is mediated by the same cis-acting element required for E2 transactivation. Inhibition of transformation may result from down-regulation of E2-dependent viral gene expression. Analysis of cDNA expressing the inhibition/repression activities mapped the function to the 3' domain of the E2 open reading frame. The E2 open reading frame thus encodes both positive and negative transcriptional regulatory factors, and these factors share a carboxy-terminal domain.

E1a inducibility of the adenoviral early E2a promoter is determined by specific combinations of sequence elements

By transient expression analysis in HeLa cells of adenovirus-2 E2a early (E2aE) promoter mutants and hybrid E2aE-beta-globin gene constructs, we demonstrate the existence of three nucleotide (nt) sequence elements involved in the E1a-responsiveness of the E2aE transcription unit: element I, localized within a segment (nt -13 to +62) surrounding the major E2aE cap site (nt + 1); element II (between nt -71 and -29), and element III (between nt -146 and -86). Each element is unable by itself to confer E1a responsiveness. Only combinations of sequences including elements I and II (spanning nt -71 and +62) or II and III (spanning nt -146 and -29) ensure maximal inducibility, for which element II appears of central importance.