The major transcriptional transactivation domain of simian virus 40 large T antigen associates nonconcurrently with multiple components of the transcriptional preinitiation complex

Abstract

Simian virus 40 (SV40) large T antigen (Tag) is a promiscuous transcriptional transactivator; however, its mechanism of transactivation remains unknown. Recent studies have suggested the possible involvement of protein-protein interactions with TBP, the TATA box-binding protein of TFIID, and TEF-1, an enhancerbinding factor. We show here that (i) the Tag domain containing amino acids 133 to 249 directly interacts with the general transcription factor TFIIB, the activator protein Sp1, and the 140-kDa subunit of RNA polymerase II, as well as with TBP and TEF-1; (ii) these interactions can also occur when these transcription factors are present in their functional states in cellular extracts; (iii) binding of Tag to TBP is eliminated by preincubation of TBP either at 48؇C or with the adenovirus 13S E1a protein; (iv) this domain of Tag cannot bind concurrently to more than one of these transcription factors; and (v) the substitution of Tag amino acid residues 173 and 174 inactivates the ability of this Tag domain both to associate with any of these transcription factors and to transactivate the SV40 late promoter. Thus, we conclude that SV40 Tag probably does not transactivate via the concurrent interaction with multiple components of the preinitiation complex. Rather, we hypothesize that transactivation by Tag may primarily occur by removing or preventing the binding of factors that inhibit the formation of preinitiation complexes.

Adding an Rb-binding site to an N-terminally truncated simian virus 40 T antigen restores growth to high cell density, and the T common region in trans provides anchorage-independent growth and rapid growth in low serum concentrations

“…A large number of activities reside in or are dependent on the N-terminal 250 amino acids of T antigen. These include binding the cellular proteins of the retinoblastoma (Rb) susceptibility family (Rb/p130/p107) (8,(11)(12)(13), a protein of unknown function (p185) (23), the heat shock 73 (Hsc73) protein (38), and the transcription factors TFIIB, Sp1, TBP, TEF-1, and the 140K subunit of RNA polymerase (2,19), as well as the nuclear localization signal (21); binding to the viral origin of replication (1); activities needed for maximal stimulation of cell DNA synthesis (9,10); and transcriptional transactivating activities (24-26, 36a, 49). Thus, it is not clear which one or several of these activities are needed to confer the altered growth properties.…”

Protein encoded by HSV‐1 stimulation‐related gene 1 (HSRG1) interacts with and inhibits SV40 large T antigen

“…LT, an essential viral replication factor, can regulate viral early and late transcription in SV40 infection (Khoury & May 1977;Hansen et al 1981;Alwine & Picardi 1986). LT also serves as a transcriptional activator of cellular promoters through direct interaction with components of transcription machines including TBP, TAPs and more to regulate cellular or viral transcription (Johnston et al 1996). Combined with the ability to inhibit p53, LT is able to drive cells into the S phase (Sladek et al 2000).…”

Generation of Mouse Osteoclastogenic Cell Lines Immortalized with SV40 Large T Antigen

“…Several studies have indicated that large T antigen can regulate cell growth, in part, by binding and inactivating the tumor suppressors proteins pRB and p53 42,43 . In addition, large T antigen can transactivate cellular genes, and this process is mediated by specific protein–protein interactions with multiple components of the transcription machinery 44–47 . These alterations in the transcriptional activity of specific cellular genes most likely play an important role in the growth‐promoting activity induced by large T antigen.…”