Repression of Activator-Mediated Transcription by Herpes Simplex Virus ICP4 via a Mechanism Involving Interactions with the Basal Transcription Factors TATA-Binding Protein and TFIIB

Abstract

Infected-cell polypeptide 4 (ICP4) of herpes simplex virus type 1 (HSV-1) is both a repressor and an activator of RNA polymerase II (Pol II) transcription. ICP4 is expressed immediately after viral infection and is essential for viral lytic growth (8, 14, 52) because of its role in the transcriptional activation of most viral early and late genes (9,15,21,48,54,65). Like many other transcriptional activators, ICP4 is composed of discrete functional domains including transactivation, repression, dimerization, nuclear localization, and DNA binding (10,11,50,51,60). ICP4 is a very large protein, existing in cells as an elongated 61). It is a sequence-specific DNA-binding protein (17,39,46) because of a DNA binding domain that contains a helix-turn-helix motif (60). The repressing activity of ICP4 has been most clearly demonstrated by the autoregulation of its own expression (9, 49, 57). The promoter for ICP4 contains a strong ICP4 binding site near the transcription start (18,39,46). Studies using transient expression assays, mutant viruses, and in vitro transcription assays have shown that ICP4 represses transcription of its own promoter as a function of this site (9,25,45,49,56). However, the exact mechanism of transcription inhibition by ICP4 is unclear.Accurate transcription by Pol II requires a number of general transcription factors, including TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIIH (4, 71). The assembly of transcription initiation complexes by the general transcription factors follows the binding of TFIID to the promoter TATA box, which results in a committed complex (4, 66). TFIID is a large multisubunit protein complex consisting of the TATA boxbinding protein (TBP) and at least 8 TBP-associated factors (TAFs) (34, 72). The addition of TFIIA, TFIIB, Pol II-TFIIF, and subsequently TFIIE and TFIIH forms the complete initiation complex (4, 71). TFIIB interacts with TBP and Pol II and is responsible for the recruitment of Pol II to the complex (27). Modulation of Pol II gene transcription involves both transcription activation and repression. In vitro reconstitution of transcription with highly fractionated and purified recombinant transcription factors has demonstrated that TBP, together with other general factors, is sufficient to direct accurate basal transcription while TFIID is required for activation by specific factors (53,64). Communication or interaction with TAFs or coactivators is required for activation by specific activator proteins. It has previously been shown that ICP4 also requires coactivators to stimulate transcription (24). Although the specific activator-TAF interactions have been clearly shown to be involved in the communication between the activators and the transcription machinery, how the communication affects the transcription machinery and leads to transcription enhancement is still unknown.Consistent with the multistep nature of the transcription process, repression of transcription can also occur at multiple steps. Repression of transcription can occur at either the basal or t...

Association of Herpes Simplex Virus Type 1 ICP8 and ICP27 Proteins with Cellular RNA Polymerase II Holoenzyme

“…EtBr, immunoprecipitation was done on untreated HSV-infected cell lysate in the presence of 50 g of ethidium bromide/ml. (12,31,82), that ICP22 is required for the aberrant modification of Pol II (48,68,69), and that ICP4 and ICP22 colocalize with Pol II in discrete nuclear structures after the onset of viral DNA replication (47), we were unable to detect these proteins in immunoprecipitates with Pol II in the anti-hSRB7 immunoprecipitates under our experiment conditions. The lack of evidence for the coprecipitation of these proteins with Pol II under these conditions does not exclude their presence in the Pol II holoenzyme complex; it could mean that they are not present in the complex, but it could also mean that they do not interact in a way that allows their recovery in the immunoprecipitate.…”

“…Late promoters have only a TATA box, an initiator element, and a downstream activating sequence (reviewed in reference 71). The HSV ICP4 protein has been shown to bind to general transcription factors and associated factors (12,31,82), and evidence for interactions between ICP4 and ICP27 has been reported (57). Thus, it is conceivable that ICP4 associates with general transcription factors and viral DNA while ICP27 associates with the Pol II complex and that the interaction between ICP4 and ICP27 brings Pol II to the viral genome for efficient transcription of late viral promoters.…”

“…The ␣ protein ICP4 is required for transcriptional activation of most, if not all, ␤ and ␥ genes (reviewed in reference 71) but represses ␣ gene expression (24,94). ICP4 is able to form complexes with the general transcription factors TFIIB, TATA-binding protein (TBP), and TBP-associated factor TAF250 (12,31,82). A second ␣ protein, ICP0, stimulates expression of all three temporal classes of HSV genes during lytic infection (11,73,88).…”

Role of the IE62 Consensus Binding Site in Transactivation by the Varicella-Zoster Virus IE62 Protein

“…Finally, no binding sites for other activators, such as Sp1 and USF, were present in the model promoters used. Thus, in contrast to ICP4 (16,17), IE62 is capable of repression of basal as well as activated transcription in the context of the consensus site.…”

Transcription of the Acanthamoeba TATA-binding Protein Gene

“…There is a third class of repressors that directly target a component(s) of the basal transcription machinery rather than inhibiting specific transcription activators. This class of repressor can destabilize or inhibit the formation of initiation complexes by targeting basal factors such as TFIID/TBP (38 -41), TFIIB (5,42), polymerase II (43), and TFIIE (44). For example, Dr1 prevents TFIIA and/or TFIIB from being recruited to the preinitiation complex by itself binding to TBP (40).…”