The 62- and 80-kDa subunits of transcription factor IIH mediate the interaction with Epstein-Barr virus nuclear protein 2

Epstein-Barr virus nuclear antigen 3C putative repression domain mediates coactivation of the LMP1 promoter with EBNA-2

The Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA-3C) regulates virus and cell genes and is essential for EBV-mediated transformation of primary B lymphocytes. EBNA-3C associates with the cellular DNA sequence-specific transcription factors RBP-Jkappa and PU.1 and coactivates the EBV LMP1 promoter with EBNA-2 in BL2 and Raji cells under conditions of restrictive growth. We now find that EBNA-3C is similar to EBNA-LP in coactivating the LMP1 promoter with EBNA-2 in non-EBV-infected Burkitt lymphoma cells under conditions of maximal cell growth, whereas the EBV Cp promoter is repressed under the same conditions. EBNA-3A and EBNA-3B coactivation are at most 40% that of EBNA-3C. The RBP-Jkappa binding sites of EBNA-2 and the LMP1 promoter are not required for EBNA-3C coactivation, whereas the PU.1 site in the LMP1 promoter is required for EBNA-2-mediated activation and EBNA-3C coactivation. EBNA-3C amino acids (aa) 365 to 545, including most of the previously identified repression domain (M. Bain, R. J. Watson, P. J. Farrell, and M. J. Allday, J. Virol. 70:2481-2489, 1996), are necessary and sufficient for coactivation with wild-type EBNA-2. EBNA-3C can also coactivate with the EBNA-2 acidic activating domain; this activation does not require aa 343 to 545. These data indicate that there are at least two mechanisms by which EBNA-3C coactivates the LMP1 promoter with EBNA-2. Of the proteins that interact with EBNA-3C in a yeast two-hybrid screen, only the ubiquitin-like proteins SUMO-1 and SUMO-3/hSMT3B map to aa 365 to 545, implicating these molecules in EBNA-3C coactivation. In addition, SUMO-1 associates at a high level with EBNA-3C in lymphoblasts. Promoter coactivation by EBNA-3C is likely to be important in ensuring adequate levels of LMP1, while inhibition of the EBNA-Cp promoter under the same conditions prevents uncontrolled up-regulation of EBNA expression from a positive-feedback loop.

Functional cooperation of Epstein-Barr virus nuclear antigen 2 and the survival motor neuron protein in transactivation of the viral LMP1 promoter

Epstein-Barr virus nuclear antigen 2 (EBNA2) is essential for viral transformation of B cells and transactivates cellular and viral target genes by binding RBPJkappa tethered to cognate promoter elements. EBNA2 interacts with the DEAD-box protein DP103 (DDX20/Gemin3), which in turn is complexed to the survival motor neuron (SMN) protein. SMN is implicated in RNA processing, but a role in transcriptional regulation has also been suggested. Here, we show that DP103 and SMN are complexed in B cells and that SMN coactivates the viral LMP promoter in the presence of EBNA2 in reporter gene assays and in vivo. Subcellular localization studies revealed that nuclear gems and/or coiled bodies containing DP103 and SMN are targeted by EBNA2. Protein-protein interaction experiments demonstrated that DP103 binds to SMN exon 6 and that both EBNA2 and SMN interact with the C terminus of DP103. Furthermore, a DP103 binding-deficient SMN mutant was released from nuclear gems and/or coiled bodies and further enhanced coactivation. In addition, impaired transactivation of a DP103 binding-deficient EBNA2 mutant was rescued by overexpression of SMN. Testing different promoter constructs in luciferase assays showed that RBPJkappa is required but not sufficient for coactivation by EBNA2 and SMN. Overall, our data suggest that EBNA2 might target spliceosomal complexes by binding to DP103, thereby releasing SMN which subsequently exerts a coactivational function within the RNA-polymerase II transcription complex on the LMP1 promoter.

Genetic analysis of the Epstein-Barr virus-coded leader protein EBNA-LP as a co-activator of EBNA2 function

Co-operation between the Epstein-Barr virus (EBV)-coded leader protein EBNA-LP and the nuclear antigen EBNA2 appears to be critical for efficient virus-induced B cell transformation. Here we report the genetic analysis of EBNA-LP function using two transient co-transfection assays of co-operativity, activation of latent membrane protein 1 (LMP1) expression from a resident EBV genome in Akata-BL cells and activation of an EBNA2-responsive reporter construct. Small deletions were introduced into each of five conserved regions (CRs) of EBNA-LP sequence present in type 1 and type 2 EBV strains and in several primate lymphocryptovirus EBNA-LP homologues. Deletions within all three CRs in the EBNA-LP W1W2 repeat domain completely abrogated function, through inhibition of nuclear localization in the cases of CR1 and CR2 but not of CR3; deletions within CR4 and CR5 in the Y1Y2 unique domain had relatively little effect, yet loss of the whole Y2 sequence blocked activity. Alanine substitution of serine residues within potential phosphorylation sites identified two mutants of particular interest. Substitution of three such residues (S34,36,63) within W1W2 not only abrogated EBNA-LP activity but was associated with a complete loss of EBNA2 detectability in co-transfected cells, implying possible destabilization of the co-expressed EBNA2 protein. More importantly the individual substitution of S36 completely blocked EBNA-LP/EBNA2 co-operativity while retaining EBNA2 expression. We infer critical roles for the CR3 domain and for the S36 residue in EBNA-LP's co-operative function.

EBNA2 and Notch signalling in Epstein-Barr virus mediated immortalization of B lymphocytes

Epstein-Barr virus (EBV) has the ability to immortalize B cells. A viral key protein for immortalization is the transactivator EBNA2 that controls expression of several viral and cellular genes. EBNA2 is tethered to promoters by interacting with the cellular repressor RBP-J. This resembles the physiological activation of RBP-J-repressed promoters by activated Notch receptors (Notch-IC). Since EBNA2 and Notch-IC have been shown to be partially interchangeable in regard to activation of target genes in B cell lines and modulation of differentiation processes it is conceivable that EBNA2 is a biological equivalent of an activated Notch receptor.

The latency-associated nuclear antigen encoded by Kaposi's sarcoma-associated herpesvirus activates two major essential Epstein-Barr virus latent promoters

The latency-associated nuclear antigen (LANA) encoded by the Kaposi's sarcoma-associated herpesvirus (KSHV) is expressed in the majority of KSHV-infected cells and in cells coinfected with Epstein-Barr virus (EBV). In coinfected body cavity-based lymphomas (BCBLs), EBV latent membrane protein 1 (LMP1), which is essential for B-lymphocyte transformation, is expressed. EBNA2 upregulates the expression of LMP1 and other cellular genes through specific interactions with cellular transcription factors tethering EBNA2 to its responsive promoters. In coinfected BCBL cells, EBNA2 is not detected but LANA, which is constitutively expressed, contains motifs suggestive of potential transcriptional activity. Additionally, recent studies have shown that LANA is capable of activating cellular promoters. Therefore, we investigated whether LANA can affect transcription from two major EBV latent promoters. In this study, we demonstrated that LANA can efficiently transactivate both the LMP1 and C promoters in the human B-cell line BJAB as well as in the human embryonic kidney 293 cell line. Moreover, we demonstrated that specific domains of LANA containing the putative leucine zipper and the glutamic acid-rich region are highly effective in upregulating these viral promoters, while the amino-terminal region (435 amino acids) exhibited little or no transactivation activity in our assays. We also specifically tested truncations of the LMP1 promoter element and showed that the -204 to +40 region had increased levels of activation compared with a larger region, -512 to +40, which contains two recombination signal-binding protein J kappa binding sites. The smaller, -204 to +40 promoter region contains specific binding sites for the Ets family transcription factor PU.1, transcription activating factor/cyclic AMP response element, and Sp1, all of which are known to function as activators of transcription. Our data therefore suggest a potential role for LANA in regulation of the major EBV latent promoters in KSHV- and EBV-coinfected cells. Furthermore, LANA may be able to activate transcription of viral and cellular promoters in the absence of EBNA2, potentially through association with transcription factors bound to their cognate sequences within the -204 to +40 region. This regulation of viral gene expression is critical for persistence of these DNA tumor viruses and most likely involved in mediating the oncogenic process in these coinfected cells.

Reconstitution of recombinant TFIIH that can mediate activator-dependent transcription

BACKGROUND

TFIIH is one of the general transcription factors required for accurate transcription of protein-coding genes by RNA polymerase II. TFIIH has helicase and kinase activities, plays a role in promoter opening and promoter escape, and is also implicated in efficient activator-dependent transcription.

RESULTS

We have established a reconstitution system of recombinant TFIIH using a three-virus baculovirus expression system. The recombinant TFIIH was active in CTD kinase and DNA helicase assays, and showed both basal and activator-dependent transcriptional activities that were indistinguishable from those of HeLa cell-derived TFIIH. Further analyses using recombinant TFIIH confirmed a critical role of TFIIH in activator-dependent transcription. The dose response of TFIIH in activator-dependent transcription suggested that mere recruitment of TFIIH is not sufficient for transcriptional activation. The sensitivity of activator-dependent transcription to nonhydrolysable ATP analogues indicated the importance of the enzymatic activities of TFIIH in transcriptional activation.

CONCLUSIONS

Our results raise a possibility that transcriptional activation by GAL4-VP16 requires enzymatic activities. Recombinant TFIIH reconstituted from this baculovirus system should be useful for analysis of the mechanisms of activation by GAL4-VP16.

The Epstein-Barr virus and post-transplant lymphoproliferative disease: interplay of immunosuppression, EBV, and the immune system in disease pathogenesis

Transplant patients are at particular risk for developing post-transplant lymphoproliferative disease (PTLD) following administration of immunosuppressive therapy. In many cases the PTLD lesions express Epstein-Barr virus (EBV) latent and lytic genes as well as elevated levels of host cytokines. An outline of the potential contributions of EBV, host cytokines and T cells, and the immunosuppressive cyclosporine A, tacrolimus, and anti-CD3 antibody in the mechanism and pathogenesis of this disease is presented and discussed.

Molecular virology of Epstein-Barr virus

Epstein-Barr virus (EBV) interacts with its host in three distinct ways in a highly regulated fashion: (i) EBV infects human B lymphocytes and induces proliferation of the infected cells, (ii) it enters into a latent phase in vivo that follows the proliferative phase, and (iii) it can be reactivated giving rise to the production of infectious progeny for reinfection of cells of the same type or transmission of the virus to another individual. In healthy people, these processes take place simultaneously in different anatomical and functional compartments and are linked to each other in a highly dynamic steady-state equilibrium. The development of a genetic system has paved the way for the dissection of those processes at a molecular level that can be studied in vitro, i.e. B-cell immortalization and the lytic cycle leading to production of infectious progeny. Polymerase chain reaction analyses coupled to fluorescent-activated cell sorting has on the other hand allowed a descriptive analysis of the virus-host interaction in peripheral blood cells as well as in tonsillar B cells in vivo. This paper is aimed at compiling our present knowledge on the process of B-cell immortalization in vitro as well as in vivo latency, and attempts to integrate this knowledge into the framework of the viral life cycle in vivo.

Direct and indirect regulation of cytokine and cell cycle proteins by EBNA-2 during Epstein-Barr virus infection

We have studied the pathways of regulation of cytokine and cell cycle control proteins during infection of human B lymphocytes by Epstein-Barr virus (EBV). Among 30 cytokine RNAs analyzed by the RNase protection assay, tumor necrosis factor alpha (TNF-alpha), granulocyte colony-stimulating factor, lymphotoxin (LT), and LTbeta were found to be regulated within 20 h of EBV infection of primary B cells. Similar results were obtained using the estrogen-regulated EBNA-2 cell line EREB2.5, in which RNAs for LT and TNF-alpha were induced within 6 h of activation of EBNA-2. Expression of Notch also caused an induction of TNF-alpha RNA. The induction of TNF-alpha RNA by EBNA-2 was indirect, and constitutive expression of either LMP-1 or c-myc proteins did not substitute for EBNA-2 in induction of TNF-alpha RNA. Cyclin D2 is also an indirect target of EBNA-2-mediated transactivation. EBNA-2 was found to activate the cyclin D2 promoter in a transient-transfection assay. A mutant of EBNA-2 that does not bind RBP-Jkappa retained some activity in this assay, and activation did not depend on the presence of B-cell-specific factors. Deletion analysis of the cyclin D2 promoter revealed that removal of sequences containing E-box c-myc consensus DNA binding sequences did not reduce EBNA-2-mediated activation of the cyclin D2 promoter in the transient-transfection assay. The results indicate that cytokines are an early target of EBNA-2 and that EBNA-2 can regulate cyclin D2 transcription in EBV-infected cells by mechanisms additional to the c-myc pathway.

EBNA-LP associates with cellular proteins including DNA-PK and HA95

EBNA-LP-associated proteins were identified by sequencing proteins that immunoprecipitated with Flag epitope-tagged EBNA-LP (FLP) from lymphoblasts in which FLP was stably expressed. The association of EBNA-LP with Hsp70 (72/73) was confirmed, and sequences of DNA-PK catalytic subunit (DNA-PKcs), HA95, Hsp27, prolyl 4-hydroxylase alpha-1 subunit, alpha-tubulin, and beta-tubulin were identified. The fraction of total cellular HA95 that associated with FLP was very high, while progressively lower fractions of the total DNA-PKcs, Hsp70, Hsp 27, alpha-tubulin, and beta-tubulin specifically associated with EBNA-LP as determined by immunoblotting with antibodies to these proteins. EBNA-LP bound to two domains in the DNA-PKcs C terminus and DNA-PKcs associated with the EBNA-LP repeat domain. DNA-PKcs that was bound to EBNA-LP phosphorylated p53 or EBNA-LP in vitro, and the phosphorylation of EBNA-LP was inhibited by Wortmannin, a specific in vitro inhibitor of DNA-PKcs.

Epstein-Barr virus nuclear protein 2 has at least two N-terminal domains that mediate self-association

Previous genetic and biochemical analyses have indicated that the Epstein-Barr virus EBNA-2 amino terminus is important for primary B-lymphocyte growth transformation and may be involved in self-association. We now report that EBNA-2 has at least two domains, amino acids 1 to 60 and 96 to 210, which independently mediate homotypic association, 1 to 60 with 1 to 60 and 96 to 210 with 96 to 210. EBNA-2 self-association is likely to be critical to the ability of EBNA-2 to interact simultaneously with multiple cellular transcription factors, coactivators, and histone acetyltransferases through its RBPJkappa binding and acidic activating domains.

Defective interplay of activators and repressors with TFIH in xeroderma pigmentosum

Inherited mutations of the TFIIH helicase subunits xeroderma pigmentosum (XP) B or XPD yield overlapping DNA repair and transcription syndromes. The high risk of cancer in these patients is not fully explained by the repair defect. The transcription defect is subtle and has proven more difficult to evaluate. Here, XPB and XPD mutations are shown to block transcription activation by the FUSE Binding Protein (FBP), a regulator of c-myc expression, and repression by the FBP Interacting Repressor (FIR). Through TFIIH, FBP facilitates transcription until promoter escape, whereas after initiation, FIR uses TFIIH to delay promoter escape. Mutations in TFIIH that impair regulation by FBP and FIR affect proper regulation of c-myc expression and have implications in the development of malignancy.

Epstein-barr virus nuclear antigen 2 retards cell growth, induces p21(WAF1) expression, and modulates p53 activity post-translationally

The Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA2) has been shown to be required for promotion of cell-cycle progression in EBV-immortalized B-lymphocytes. However, other studies have indicated that EBNA2 alone, in the absence of other EBV genes, may retard cell growth. To resolve this discrepancy, we investigated the effect of EBNA2 on the growth of various cells, including EBV target nasopharyngeal carcinoma cells, NPC-TW01 and NPC-TW04. We found that EBNA2 could retard cell growth, in stable Vero, HEp-2, and U2OS cell clones expressing EBNA2, and in Vero, 293, NPC-TW01, and NPC-TW04 cells transiently transfected with EBNA2. While investigating the mechanism underlying the growth-retarding function of EBNA2, we found that EBNA2 induced p21(WAF1) expression in these cells. This induction of p21(WAF1) expression was mediated through p53. EBNA2 was found to stimulate p53 to bind to the p53-response element within the p21(WAF1) promoter, possibly by promoting p53 phosphorylation. This enhancement of p53 sequence-specific DNA-binding activity may be the mechanism through which EBNA2 activates the expression of p53-regulated genes, including p21(WAF1) and mdm-2. Together, these studies reveal a possible intrinsic function of EBNA2 in cell-growth regulation and elucidate a novel mechanism by which EBNA2 modulates transcription.

Promoter-specific targeting of human SWI-SNF complex by Epstein-Barr virus nuclear protein 2

The multiprotein human SWI-SNF (hSWI-SNF) complex is a chromatin-remodeling machine that facilitates transcription by overcoming chromatin-mediated gene repression. We had previously shown that hSNF5/INI1, an intrinsic, consistent component of the hSWI/SNF complex, is associated with Epstein-Barr nuclear antigen 2 (EBNA2) and have proposed that EBNA2 directs this complex to key EBNA2-responsive viral and cellular genes. Using chromatin immunoprecipitation and quantitative PCR, we show that antibodies directed against components of the hSWI-SNF complex preferentially precipitate chromatin-associated DNA that contains a targeted EBNA2-responsive element in the context of both episomal and cellular chromatin. This enrichment does not occur in EBNA2-negative cells or when the EBNA2-responsive element is mutated. The stable association of the hSWI-SNF complex with the EBNA2-responsive promoter can also be disrupted by deletion of the TATA element, suggesting that EBNA2 in itself is insufficient to mediate stable targeting of the hSWI-SNF complex. These results demonstrate that recruitment of the hSWI-SNF complex to selected promoters can occur in vivo through its interaction with site-specific activator proteins and that stable targeting may require the presence of basal transcription factors.

Epstein-barr virus nuclear antigen 3C activates the latent membrane protein 1 promoter in the presence of Epstein-Barr virus nuclear antigen 2 through sequences encompassing an spi-1/Spi-B binding site

The Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA-3C) protein is a transcriptional regulator of viral and cellular genes that is essential for EBV-mediated immortalization of B lymphocytes in vitro. EBNA-3C can inhibit transcription through an association with the cellular DNA-binding protein Jkappa, a function shared by EBNA-3A and EBNA-3B. Here, we report a mechanism by which EBNA-3C can activate transcription from the EBV latent membrane protein 1 (LMP-1) promoter in conjunction with EBNA-2. Jkappa DNA-binding sites were not required for this activation, and a mutant EBNA-3C protein unable to bind Jkappa activated transcription as efficiently as wild-type EBNA-3C, indicating that EBNA-3C can regulate transcription through a mechanism that is independent of Jkappa. Furthermore, activation of the LMP-1 promoter is a unique function of EBNA-3C, not shared by EBNA-3A and EBNA-3B. The DNA element through which EBNA-3C activates the LMP-1 promoter includes a Spi-1/Spi-B binding site, previously characterized as an important EBNA-2 response element. Although this element has considerable homology to mouse immunoglobulin light chain promoter sequences to which the mouse homologue of Spi-1 binds with its dimerization partner IRF4, we demonstrate that the IRF4-like binding sites in the LMP-1 promoter do not play a role in EBNA-3C-mediated activation. Both EBNA-2 and EBNA-3C were required for transcription mediated through a 41-bp region of the LMP-1 promoter encompassing the Spi binding site. However, EBNA-3C had no effect on transcription mediated in conjunction with the EBNA-2 activation domain fused to the GAL4 DNA-binding domain, suggesting that it does not function as an adapter between EBNA-2 and the cellular transcriptional machinery. Like EBNA-2, EBNA-3C bound directly to both Spi-1 and Spi-B in vitro. This interaction was mediated by a region of EBNA-3C encompassing a likely basic leucine zipper (bZIP) domain and the ets domain of Spi-1 or Spi-B, reminiscent of interactions between bZIP and ets domains of other transcription factors that result in their targeting to DNA. There are many examples of regulation of the hematopoietic-specific Spi transcription factors through protein-protein interactions, and a similar regulation by EBNA-3C, in conjunction with EBNA-2, is likely to be an important and unique contribution of EBNA-3C to EBV-mediated immortalization.

The FBP interacting repressor targets TFIIH to inhibit activated transcription

FUSE-binding protein (FBP) binds the single-stranded far upstream element of active c-myc genes, possesses potent transcription activation and repression domains, and is necessary for c-myc expression. A novel 60 kDa protein, the FBP interacting repressor (FIR), blocked activator-dependent, but not basal, transcription through TFIIH. Recruited through FBP's nucleic acid-binding domain, FIR formed a ternary complex with FBP and FUSE. FIR repressed a c-myc reporter via the FUSE. The amino terminus of FIR contained an activator-selective repression domain capable of acting in cis or even in trans in vivo and in vitro. The repression domain of FIR targeted only TFIIH's p89/XPB helicase, required at several stages in transcription, but not factors required for promoter selection. Thus, FIR locks TFIIH in an activation-resistant configuration that still supports basal transcription.

A role for SKIP in EBNA2 activation of CBF1-repressed promoters

EBNA2 is essential for Epstein-Barr virus (EBV) immortalization of B lymphocytes. EBNA2 functions as a transcriptional activator and targets responsive promoters through interaction with the cellular DNA binding protein CBF1. We have examined the mechanism whereby EBNA2 overcomes CBF1-mediated transcriptional repression. A yeast two-hybrid screen performed using CBF1 as the bait identified a protein, SKIP, which had not previously been recognized as a CBF1-associated protein. Protein-protein interaction assays demonstrated contacts between SKIP and the SMRT, CIR, Sin3A, and HDAC2 proteins of the CBF1 corepressor complex. Interestingly, EBNA2 also interacted with SKIP in glutathione S-transferase affinity and mammalian two-hybrid assays and colocalized with SKIP in immunofluorescence assays. Interaction with SKIP was not affected by mutation of EBNA2 conserved region 6, the CBF1 interaction region, but was abolished by mutation of conserved region 5. Mutation of conserved region 5 also severely impaired EBNA2 activation of a reporter containing CBF1 binding sites. Thus, interaction with both CBF1 and SKIP is necessary for efficient promoter activation by EBNA2. A model is presented in which EBNA2 competes with the SMRT-corepressor complex for contacts on SKIP and CBF1.

Intracellular forms of human NOTCH1 functionally activate essential Epstein-Barr virus major latent promoters in the Burkitt's lymphoma BJAB cell line but repress these promoters in Jurkat cells

We have demonstrated that intracellular forms of NOTCH1 transactivate two major Epstein-Barr virus (EBV) latent promoters, the LMP1 and Cp1 promoters in an EBV-negative B-cell line, BJAB. Truncated intracellular NOTCH1 associated with the nuclear membrane (DeltaE) transactivates the LMP1 promoter fivefold; however, the intranucleus localized form of NOTCH1 (ICN) transactivates this promoter approximately twofold in chloroamphenicol acetyltransferase (CAT) reporter assays in BJAB cells. Additionally, DeltaE activated the major Cp1 promoter 12-fold, whereas the ICN form of NOTCH1 activates at only about half that level when compared to that of DeltaE membrane-bound NOTCH1. This result differs from previously observed data, where intracellular NOTCH1 bound to the nuclear membrane, DeltaE, and nucleus-localized NOTCH1, ICN, all had similar levels of activation in 293 cells. This suggests distinct transcriptional activities in different cell types. Moreover, in Jurkat cells, a T-cell line, intranucleus localized NOTCH1 molecules demonstrated a repressive activity against the two EBV major latent promoters. Only DeltaE activated the Cp1 and LMP1 promoters at a level slightly above background, whereas intranucleus localized NOTCH1 ICN, or the form of NOTCH1 lacking the ankyrin repeats, DeltaE(TAR), surprisingly resulted in the repression of these promoters in Jurkat cells. Similarly, another truncated form of NOTCH1, referred to as ICNW, which contains the tryptophan residue W(1767) within one of the RBP-Jkappa interacting domains, repressed the LMP1 promoter approximately twofold. Further analysis of the truncated NOTCH1 molecules on the LMP1 promoter element, lacking the two RBP-Jkappa binding sites, suggests that repression in Jurkat cells may be affected by the presence of the two RBP-Jkappa binding sites. These studies indicate that intracellular NOTCH1 can activate the EBV major latent promoters in BJAB cells. However, in Jurkat cells, intracellular truncated forms of NOTCH1 lacking the RBP-Jkappa binding sites repress these EBV latent promoters. Only the membrane-bound form of NOTCH1, DeltaE, activated the EBV major latent promoters in Jurkat cells, albeit at a lower level than that seen in BJAB cells. Our data suggest that EBNA2 and truncated intracellular nuclear localized forms of NOTCH1 may be functionally similar in their interactions with RBP-Jkappa; however, these molecules may have distinctly different transcriptional partners in BJAB and Jurkat cells. Moreover, these truncated NOTCH1 molecules may not represent the normal processed forms of NOTCH1 in cells and may exhibit dominant negative phenotypes in the absence of the required posttranslational modifications. Further investigations are necessary to determine the similarity and differences occurring with intracellular NOTCH1 in other B- and T-cell lines.

Epstein-Barr virus nuclear protein 2 interacts with p300, CBP, and PCAF histone acetyltransferases in activation of the LMP1 promoter

The Epstein-Barr virus (EBV) nuclear protein 2 (EBNA2) and herpes simplex virion protein 16 (VP16) acidic domains that mediate transcriptional activation now are found to have affinity for p300, CBP, and PCAF histone acetyltransferases (HATs). Transcriptionally inactive point mutations in these domains lack affinity for p300, CBP, or PCAF. P300 and CBP copurify with the principal HAT activities that bind to EBNA2 or VP16 acidic domains through velocity sedimentation and anion-exchange chromatography. EBNA2 binds to both the N- and C-terminal domains of p300 and coimmune-precipitates from transfected 293T cells with p300. In EBV-infected Akata Burkitt's tumor cells that do not express the EBV encoded oncoproteins EBNA2 or LMP1, p300 expression enhances the ability of EBNA2 to up-regulate LMP1 expression. Through its intrinsic HAT activity, PCAF can further potentiate the p300 effect. In 293 T cells, P300 and CBP (but not PCAF) can also coactivate transcription mediated by the EBNA2 or VP16 acidic domains and HAT-negative mutants of p300 have partial activity. Thus, the EBNA2 and VP16 acidic domains can utilize the intrinsic HAT or scaffolding properties of p300 to activate transcription.

The proto-oncogene c-myc is a direct target gene of Epstein-Barr virus nuclear antigen 2

Epstein-Barr virus (EBV) infects and transforms primary B lymphocytes in vitro. Viral infection initiates the cell cycle entry of the resting B lymphocytes. The maintenance of proliferation in the infected cells is strictly dependent on functional EBNA2. We have recently developed a conditional immortalization system for EBV by rendering the function of EBNA2, and thus proliferation of the immortalized cells, dependent on estrogen. This cellular system was used to identify early events preceding induction of proliferation. We show that LMP1 and c-myc are directly activated by EBNA2, indicating that all cellular factors essential for induction of these genes by EBNA2 are present in the resting cells. In contrast, induction of the cell cycle regulators cyclin D2 and cdk4 are secondary events, which require de novo protein synthesis.

Residues 231 to 280 of the Epstein-Barr virus nuclear protein 2 are not essential for primary B-lymphocyte growth transformation

Epstein-Barr virus (EBV) nuclear protein 2 (EBNA-2) is a transcriptional transactivator of cellular and viral gene expression and is essential for the transformation of resting human B lymphocytes into long-term lymphoblastoid cell lines (LCLs). Previous molecular genetic analyses identified three domains that are critical for transformation and showed that the rest of EBNA-2 is not critical. We now find that codons 231 to 280 that were part of one of the critical domains (J. I. Cohen, F. Wang, and E. Kieff, J. Virol. 65:2545-2554, 1991) can be deleted with only a small effect on the ability of EBNA-2 to transactivate gene expression. In transient transfection assays, EBNA-2 deleted for codons 231 to 280 accumulated to higher levels and was similar to wild-type EBNA-2 in activation of the BamC promoter and in association with RBPJk, a cellular transcription factor that is important for EBNA-2 interaction with promoter regulatory elements. However, EBNA-2 d231-280 activated the viral latent membrane protein 1 (LMP1) promoter with only 60% of wild-type efficiency. Recombinant EBVs specifically deleted for EBNA-2 codons 231 to 280 were efficient in initiating the transformation of resting primary human B lymphocytes into LCLs. However, these LCLs grew less well than wild-type EBV-transformed LCLs, and 4- to 10-fold more cells were required for outgrowth following limit dilution. EBNA-2 d231-280 accumulated to unusually high levels in the recombinant transformed LCLs, and this was associated with somewhat higher EBNA-1 and lower LMP1 expression, consistent with the near-wild-type activation of the BamC EBNA promoter and the abnormally low activation of the LMP1 promoter in transient transfection assays. Thus, EBNA-2 d231-280 modestly perturbed the regulation of viral gene expression and resulted in less LMP1, while having surprisingly subtle effects on LCL outgrowth. Deletion of EBNA-2 codons 292 to 310, which are closer to the site that specifies interaction with RBPJk, was more disruptive of RBPJk association and of the ability to transform B lymphocytes.

An interplay between TATA box-binding protein and transcription factors IIE and IIA modulates DNA binding and transcription

The basal transcription factor IIE (TFIIE) is thought to be one of the last factors to be assembled into a preinitiation complex (PIC) at eukaryotic promoters after RNA polymerase II and TFIIF have been incorporated. It was shown that a primary function of TFIIE is to recruit and cooperate with TFIIH in promoter melting. Here, we show that the large subunit of TFIIE (E56) can directly stimulate TBP binding to the promoter in the absence of other basal factors. The zinc-finger domain of E56, required for transcriptional activity, is critical for this function. In addition, the small subunit of TFIIE (E34) directly contacts DNA and TFIIA and thus providing a second mechanism for TFIIE to help binding of a TBP/IIA complex to the promoter, the first critical step in the PIC assembly. These studies suggest an alternative PIC assembly pathway in which TFIIE affects both TBP and TFIIH functions during initiation of RNA synthesis.

An ATF/CRE element mediates both EBNA2-dependent and EBNA2-independent activation of the Epstein-Barr virus LMP1 gene promoter

The Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) is a viral oncogene whose expression is regulated by both viral and cellular factors. EBV nuclear antigen 2 (EBNA2) is a potent transactivator of LMP1 expression in human B cells, and several EBNA2 response elements have been identified in the promoter regulatory sequence (LRS). We have previously shown that an activating transcription factor/cyclic AMP response element (ATF/CRE) site in LRS is involved in EBNA2 responsiveness. We now establish the importance of the ATF/CRE element by mutational analysis and show that both EBNA2-dependent activation and EBNA2-independent activation of the promoter occur via this site but are mediated by separate sets of factors. An electrophoretic mobility shift assay (EMSA) with specific antibodies showed that the ATF-1, CREB-1, ATF-2 and c-Jun factors bind to the site as ATF-1/CREB-1 and ATF-2/c-Jun heterodimers whereas the Sp1 and Sp3 factors bind to an adjacent Sp site. Overexpression of ATF-1 and CREB-1 in the cells by expression vectors demonstrated that homodimeric as well as heterodimeric forms of the factors transactivate the LMP1 promoter in an EBNA2-independent manner. The homodimers of ATF-2 and c-Jun did not significantly stimulate promoter activity. In contrast, the ATF-2/c-Jun heterodimer had only a minor stimulatory effect in the absence of EBNA2 but induced a strong transactivation of the LMP1 promoter when coexpressed with this protein. Evidence for a direct interaction between the ATF-2/c-Jun heterodimeric complex and EBNA2 was obtained by EMSA and coimmunoprecipitation experiments. Thus, our results suggest that EBNA2-induced transactivation via the ATF/CRE site occurs through a direct contact between EBNA2 and an ATF-2/c-Jun heterodimer. EBNA2-independent promoter activation via this site, on the other hand, is mediated by a heterodimeric complex between the ATF-1 and CREB-1 factors.

Characterization of the CBF2 binding site within the Epstein-Barr virus latency C promoter and its role in modulating EBNA2-mediated transactivation

The Epstein-Barr virus (EBV) EBNA2 protein is a transcriptional activator that regulates viral and cellular gene expression and is also essential for EBV-driven immortalization of B lymphocytes. The EBNA2-responsive enhancer in the viral latency C promoter (Cp) binds two cellular factors, CBF1 and CBF2. The precise role of the CBF2 protein for Cp enhancer function is presently unclear. CBF2 does not appear to interact with EBNA2 and binds just downstream of CBF1 between positions -339 and -368 in the Cp EBNA2 enhancer. Within this region an 8-bp sequence, CAGTGCGT, can be found, and a similar sequence is also located downstream of CBF1 binding sites in other EBNA2-responsive promoters. Previous studies have indicated that mutations and methylation in this sequence affect EBNA2 responsiveness. To investigate the requirements for CBF2 binding, we synthesized a series of oligonucleotides carrying double transversion mutations spanning both the conserved core sequence and outside flanking sequences. Surprisingly, mutations outside of the conserved core sequence in 4 bases immediately flanking the 5' end, GGTT, had the most deleterious effect on CBF2 binding. Mutations in the conserved core had a gradient effect, with those near the 5' end having the most deleterious effects on CBF2 binding. In addition, the affinities of CBF2 for binding to the LMP-1, LMP-2, and CD23 promoters were also measured. These promoters contain the conserved core but lack the 5' flanking GGTT motif and bound CBF2 weakly or not at all. Using Cp reporter plasmids containing CBF2 mutant binding sites, we were also able to show that at lower doses of EBNA2, Cp transactivation required a functional CBF2 binding site but that higher doses of EBNA2 transactivated CBF2 mutant promoters to 40% of wild-type levels. These assays indicate that CBF2 is important for EBNA2-mediated transactivation of the viral latency Cp. In addition, CBF2 activity was found to be associated with two polypeptides of 27 and 33 kDa.

The cyclin-dependent kinase-activating kinase (CAK) assembly factor, MAT1, targets and enhances CAK activity on the POU domains of octamer transcription factors

Octamer binding transcription factors (Oct factors) play important roles in activation of transcription of various genes but, in some cases, require cofactors that interact with the DNA binding (POU) domain. In the present study, a yeast two-hybrid screen with the Oct-1 POU domain as a bait identified MAT1 as a POU domain-binding protein. MAT1 is known to be required for the assembly of cyclin-dependent kinase (CDK)-activating kinase (CAK), which is functionally associated with the general transcription factor IIH (TFIIH). Further analyses showed that MAT1 interacts with POU domains of Oct-1, Oct-2, and Oct-3 in vitro in a DNA-independent manner. MAT1-containing TFIIH was also shown to interact with POU domains of Oct-1 and Oct-2. MAT1 is shown to enhance the ability of a recombinant CDK7-cyclin H complex (bipartite CAK) to phosphorylate isolated POU domains, intact Oct-1, and the C-terminal domain of RNA polymerase II, but not the originally defined substrate, CDK2. Phosphopeptide mapping indicates that the site (Ser385) of a mitosis-specific phosphorylation that inhibits Oct-1 binding to DNA is not phosphorylated by CAK. However, one CAK-phosphorylated phosphopeptide comigrates with a Cdc2-phosphorylated phosphopeptide previously shown to be mitosis-specific, suggesting that, in vitro, CAK is able to phosphorylate at least one site that is also phosphorylated in vivo. These results suggest (i) that interactions between POU domains and MAT1 can target CAK to Oct factors and result in their phosphorylation, (ii) that MAT1 not only functions as a CAK assembly factor but also acts to alter the spectrum of CAK substrates, and (iii) that a POU-MAT1 interaction may play a role in the recruitment of TFIIH to the preinitiation complex or in subsequent initiation and elongation reactions.

Epstein-Barr virus nuclear protein LP stimulates EBNA-2 acidic domain-mediated transcriptional activation

Epstein-Barr virus (EBV) nuclear proteins EBNA-LP and EBNA-2 are the first two proteins expressed in latent infection of primary B lymphocytes. EBNA-2 is essential for lymphocyte transformation, and EBNA-LP is at least critical. While EBNA-2 activates specific viral and cellular promoters, EBNA-LP's role has been obscure. We now show that EBNA-LP stimulates EBNA-2 activation of the LMP1 promoter and of the LMP1/LMP2B bidirectional transcriptional regulatory element. EBNA-LP alone has only a negative effect. EBNA-LP also stimulates EBNA-2 activation of a multimerized regulatory element from the BamC EBNA promoter. Since both viral regulatory elements can bind the EBNA-2-associated cell protein RBPJ kappa, consensus RBPJ kappa binding sites were positioned upstream of the herpes simplex virus type 1 thymidine kinase promoter and were found to be sufficient for EBNA-LP and EBNA-2 coactivation. EBNA-LP strongly stimulated activation of an adenovirus E1b promoter with upstream Gal4 binding sites by a Gal4 DNA binding domain/ EBNA-2 acidic domain fusion protein, indicating that EBNA-LP coactivation requires only the EBNA-2 acidic domain to be localized near a promoter. The EBNA-LP stimulatory activity resides in the amino-terminal 66-amino-acid repeat domain. The carboxyl-terminal unique 45 amino acids appear to regulate EBNA-LP's effects. The first 11 amino acids of the 45 have a strong negative effect, while the last 10 are critical for the ability of the last 34 to relieve the negative effect. These results indicate that EBNA-LP's critical role in EBV-mediated cell growth transformation is in stimulating (and probably regulating) EBNA-2-mediated transcriptional activation.

Importance of acidic, proline/serine/threonine-rich, and GTP-binding regions in the major histocompatibility complex class II transactivator: generation of transdominant-negative mutants

The class II transactivator (CIITA) is a master transcription regulator of gene products involved in the exogenous antigen presentation pathway, including major histocompatibility complex (MHC) class II, invariant chain, and DM. An extensive analysis of the putative functional domains of CIITA is undertaken here to explore the action of CIITA. Antibodies to CIITA protein were produced to verify that these mutant proteins are expressed. Both acidic and proline/serine/threonine-rich domains are essential for class II MHC promoter activation. In addition, three guanine nucleotide-binding motifs are essential for CIITA activity. Of these mutants, two exhibited strong transdominant-negative functions. These two mutants provide a plausible approach to manipulate MHC class II expression and immune responses.

Identification of seven hydrophobic clusters in GCN4 making redundant contributions to transcriptional activation

GCN4 is a transcriptional activator in the bZIP family that regulates amino acid biosynthetic genes in the yeast Saccharomyces cerevisiae. The N-terminal 100 amino acids of GCN4 contains a potent activation function that confers high-level transcription in the absence of the centrally located acidic activation domain (CAAD) delineated in previous studies. To identify specific amino acids important for activation by the N-terminal domain, we mutagenized a GCN4 allele lacking the CAAD and screened alleles in vivo for reduced expression of the HIS3 gene. We found four pairs of closely spaced phenylalanines and a leucine residue distributed throughout the N-terminal 100 residues of GCN4 that are required for high-level activation in the absence of the CAAD. Trp, Leu, and Tyr were highly functional substitutions for the Phe residue at position 45. Combined with our previous findings, these results indicate that GCN4 contains seven clusters of aromatic or bulky hydrophobic residues which make important contributions to transcriptional activation at HIS3. None of the seven hydrophobic clusters is essential for activation by full-length GCN4, and the critical residues in two or three clusters must be mutated simultaneously to observe a substantial reduction in GCN4 function. Numerous combinations of four or five intact clusters conferred high-level transcription of HIS3. We propose that many of the hydrophobic clusters in GCN4 act independently of one another to provide redundant means of stimulating transcription and that the functional contributions of these different segments are cumulative at the HIS3 promoter. On the basis of the primacy of bulky hydrophobic residues throughout the activation domain, we suggest that GCN4 contains multiple sites that mediate hydrophobic contacts with one or more components of the transcription initiation machinery.

Hepatitis B virus transactivator protein, HBx, associates with the components of TFIIH and stimulates the DNA helicase activity of TFIIH

Human hepatitis B virus genome encodes a protein, termed HBx, that is widely recognized as a transcriptional transactivator. While HBx does not directly bind cis-acting transcriptional control elements, it has been shown to associate with cellular proteins that bind DNA. Because HBx transactivated a large number of viral/cellular transcriptional control elements, we looked for its targets within the components of the basal transcriptional machinery. This search led to the identification of its interactions with TFIIH. Here, we show that HBx interacts with yeast and mammalian TFIIH complexes both in vitro and in vivo. These interactions between HBx and the components of TFIIH are supported by several lines of evidence including results from immunoprocedures and direct methods of measuring interactions. We have identified ERCC3 and ERCC2 DNA helicase subunits of holoenzyme TFIIH as targets of HBx interactions. Furthermore, the DNA helicase activity of purified TFIIH from rat liver and, individually, the ERCC2 component of TFIIH is stimulated in the presence of HBx. These observations suggest a role for HBx in transcription and DNA repair.

Epstein-Barr virus nuclear protein 2 (EBNA2) binds to a component of the human SNF-SWI complex, hSNF5/Ini1

Epstein-Barr nuclear antigen 2 (EBNA2), one of the six viral nuclear proteins expressed in latently infected B lymphocytes, is essential to the immortalization of B cells by Epstein-Barr virus (EBV). EBNA2 promotes transcriptional transactivation of viral and cellular genes by acting as an adapter molecule that binds to cellular sequence-specific DNA-binding proteins, JK recombination signal-binding protein (RBP-JK), and PU.1 and engages multiple members of the RNA polymerase II transcription complex. In the present study, we show that EBNA2 also interacts with hSNF5/Ini1, the human homolog of the yeast transcription factor SNF5. Gel filtration fractionation of partially purified EBV-positive lymphocyte nuclear extracts shows that a fraction of EBNA2 coelutes with both hSNF5/Ini1 and BRG1, a human homolog of SWI/SNF2, in the high-molecular-mass region (1.5 to 2.0 MDa) of a Superose 6 chromatogram. An affinity-purified rabbit antibody directed against hSNF5/Ini1 coimmunoprecipitates EBNA2 from this high-molecular-mass nuclear protein fraction, demonstrating that EBNA2 and hSNF5/Ini1 interact in vivo. This interaction is restricted to a subpopulation of phosphorylated viral EBNA2. Deletion mutation analysis of EBNA2 shows that the proline-rich aminoterminal end and a domain within the divergent region of EBNA2 mediate EBNA2-hSNF5/Ini1 interaction. Since the SNF-SWI complex participates in gene regulation through the alteration of nucleosome configuration and may be a component of the RNA polymerase II holoenzyme, the EBNA2-hSNF5/Ini1 interaction supports the hypothesis that EBNA2 facilitates transcriptional transactivation by acting as a transcription adapter molecule. We postulate that EBNA2 engages the hSNF-SWI complex to generate an open chromatin conformation at the EBNA2-responsive target genes, thereby potentiating the function of the RBP-JK-EBNA2-polymerase II transcription complex.

Glial and muscle embryonal carcinoma cell-specific independent regulation of expression of human JC virus early promoter by cyclic AMP response elements and adjacent nuclear factor 1 binding sites

The human polyoma JC virus (JCV) is a glial cell-specific virus and is the etiological agent for the terminal AIDS-associated brain disease, progressive multifocal leukoencephalopathy (PML). JCV contains several binding sites for transcriptional factors that are important for activity in glial cells, including cyclic AMP (cAMP) response elements (CREs) which are four nucleotides from nuclear factor 1 (NF1) sites within the two 98 bp repeat regions. We studied the combined role of cAMP and NF1 in regulating the expression of the JCV early promoter-enhancer (JCVE) in differentiating glial and muscle P19 embryonal carcinoma cells. JCVE expression remained several-fold higher in the presence of cAMP in glial cells, irrespective of whether the relatively strong activity of JCVE was greatly reduced by NF1 site mutations. In contrast, cAMP had no effect in muscle cells, independent of whether the modest activity of JCVE was two-fold higher due to NF1 site mutations. The in vivo effects were confirmed with in vitro transcription assays using glial cell extracts, competitors of CRE, and the NF1 site, and single repeat JCVE region with mutations in the NF1 II/ III binding sites as templates. The in vitro results also indicated that the effects were due to the CREs of JCV, rather than to the indirect effects of cAMP. Overall, the results indicated that NF1 and cAMP have independent, different, tissue-specific, and direct effects in the regulation of JCVE. These effects may contribute the neurotropic PML-inducing pattern of expression of JCVE.

EBNA-2 and EBNA-3C extensively and mutually exclusively associate with RBPJkappa in Epstein-Barr virus-transformed B lymphocytes

Although genetic and biochemical data indicate that the cell protein RBPJkappa is a mediator of EBNA-2 and EBNA-3C effects on transcriptional regulatory elements, the extent of association of these Epstein-Barr virus nuclear proteins with RBPJkappa in transformed B lymphocytes has not been determined. We now report that most of the EBNA-2 and at least 20% of the EBNA-3C coimmunoprecipitated with RBPJkappa from extracts of transformed B lymphocytes that contained most of the cellular EBNA-2 and EBNA3C. Both proteins are associated preferentially with the smaller of the two RBPJkappa isoforms. EBNA-2-RBPJkappa complexes do not contain EBNA-3C, and EBNA-3C-RBPJkappa complexes do not contain EBNA-2. Although EBNA-2 and EBNA-3C are extensively associated with RBPJkappa, a fraction of RBPJkappa appears to be free of EBNAs after repeated immunoprecipitations with anti-EBNA, Epstein-Barr virus-immune, human antibody. Promoters with RBPJkappa sites in their regulatory elements are likely to be differentially regulated by these RBPJkappa-EBNA-2 and RBPJkappa-EBNA-3 complexes.

Fos-Jun dimerization promotes interaction of the basic region with TFIIE-34 and TFIIF

The regulation of RNA polymerase II-mediated transcription involves both direct and indirect interactions among regulatory proteins and the general transcription factors (GTFs) that assemble at TATA-containing promoters. Here we show that the oncogenic transcription factors Fos and Jun make direct physical contacts with three proteins of the basal transcription apparatus, TFIIE-34 (TFIIE-beta), TFIIF-30 (RAP30), and TFIIF-74 (RAP74). The interactions among the activator proteins and these three GTFs were not detected with other transcription factors, including some bZIP protein family members. Both coimmunoprecipitation and protein blotting experiments demonstrated that the interactions were strongly favored by dimerization of Fos and Jun and that they involved the basic region and basic region-proximal domain of both proteins. Mutations within the DNA-binding domains of Fos and Jun abolished binding to GTFs, although the presence of DNA was not required for the association. Surprisingly, only a single basic region in the context of a protein dimer was sufficient for the interaction. Squelching of AP-1-dependent transcription in vitro by an excess of Fos-Jun dimers was relieved by the addition of TFIIE, indicating that it is a direct functional target of Fos and Jun. These results suggest that dimerization induces a conformational alteration in the basic region of Fos and Jun that promotes an association with TFIIE-34 and TFIIF, thus contributing to transcription initiation.

p53: puzzle and paradigm

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The N-terminal half of EBNA2, except for seven prolines, is not essential for primary B-lymphocyte growth transformation

Previous molecular genetic analyses of Epstein-Barr virus nuclear protein 2 (EBNA2) identified a negative effect of deletion of codons 19 to 33 on transformation and gene transactivation, while deletion of codons 19 to 110 was a null mutation for transformation and gene transactivation. We here report the surprising finding that codons 2 to 88, which encode the highly conserved unique N terminus (amino acids 1 to 58) and most of the polyproline repeat (amino acids 59 to 95), can be deleted with only minimal effects on transformation. Codons 97 to 122 can also be deleted with only minimal effects on transformation. However, deletion of 35 of the 37 prolines (amino acids 59 to 93) or deletion of codons 2 to 95 results in a null transforming phenotype. Although EBNA2 from which codons 59 to 93 were deleted was a null mutation for transformation, it was similar to some transforming mutants of EBNA2 in abundance, in interaction with RBPJK, and in transactivation of the LMP1 promoter in transient transfection assays. These data indicate that between three and seven prolines are critical for EBNA2 structure or for intermolecular interaction. Aside from these seven prolines, codons encoding the rest of the N-terminal half (amino acids 2 to 230) of EBNA2 are nonessential for primary B-lymphocyte growth transformation.

Functional interactions between p53 and the TFIIH complex are affected by tumour-associated mutations

The p53 tumour suppressor is mutated in the majority of human tumours. p53's proposed role as the guardian of the genome is reflected in its multiple effects on transcription genome stability, cell growth and survival. We show that p53 interacts both physically and functionally with the TFIIH complex. There are multiple protein-protein contacts, involving two regions of p53 and three subunits of TFIIH, ERCC2 (XPD), ERCC3 (XPB) and p62. p53 and its C-terminus (amino acids 320-393) inhibit both of the TFIIH helicases and in vitro transcription in the absence of TFIIH. Transcription inhibition is overcome by TFIIH. The N-terminal region of p53 (1-320), lacking the C-terminus, is inactive on its own, yet apparently affects the activity of the C-terminus in the native protein. Interestingly, mutant p53s that are frequently found in tumours are less efficient inhibitors of the helicases and transcription. We hypothesize that the interactions provide an immediate and direct link for p53 to the multiple functions of TFIIH in transcription, DNA repair and possibly the cell cycle.

Opening of an RNA polymerase II promoter occurs in two distinct steps and requires the basal transcription factors IIE and IIH

We have studied promoter opening in assays reconstituted with purified RNA polymerase II and basal transcription factors. We found that creating a region of heteroduplex DNA around the start site of the adenovirus major late (AdML) promoter circumvents the requirement for TFIIE and TFIIH in transcription. The critical size and position of the heteroduplex region that alleviates the requirement for TFIIE and TFIIH is six nucleotides, from -4 to +2. Promoter opening was investigated directly with potassium permanganate (KMnO4), a chemical probe specific for single-stranded thymidines. We found that KMnO4-detectable opening of the AdML promoter requires the presence of the complete pre-initiation complex, DBpolFEH, and that opening occurs in two discrete steps. First, dependent on ATP but prior to initiation, the -9 to +1 region becomes single-stranded. Second, formation of the first phosphodiester bond results in expansion of the open region to the +8 position. Our results lead to a model in which the critical function of the TFIIH-associated DNA helicases is to create a single-stranded region. This gives RNA polymerase II access to the nucleotides of the template strand and allows expansion of the open region upon formation of the first phosphodiester bond.

The Epstein-Barr virus nuclear protein 2 acidic domain forms a complex with a novel cellular coactivator that can interact with TFIIE

Epstein-Barr virus nuclear antigen 2 (EBNA 2) activates transcription of specific genes and is essential for B-lymphocyte transformation. EBNA 2 has an acidic activation domain which interacts with general transcription factors TFIIB, TFIIH, and TAF40. We now show that EBNA 2 is specifically bound to a novel nuclear protein, p100, and that p100 can coactivate gene expression mediated by the EBNA 2 acidic domain. The EBNA 2 acidic domain was used to affinity purify p100. cDNA clones encoding the p100 open reading frame were identified on the basis of peptide sequences of the purified protein. Antibody against p100 coimmunoprecipitated p100 and EBNA 2 from Epstein-Barr virus-transformed lymphocyte extracts, indicating that EBNA 2 and p100 are complexed in vivo. p100 overexpression in cells specifically augmented EBNA 2 acidic domain-mediated activation. The coactivating effect is probably mediated by p100 interaction with TFIIE. Bacterially expressed p100 specifically adsorbs TFIIE from nuclear extracts, and in vitro-translated p56 or p34 TFIIE subunit can independently bind to p100. p100 also appears to be essential for normal cell growth, since cell viability was reduced by antisense p100 RNA and restored by sense p100 RNA expression.