THE MAJOR TRANSCRIPTIONAL TRANSACTIVATION DOMAIN OF SINIAN VIRUS-40 LARGE T-ANTIGEN ASSOCIATES NONCONCURRENTLY WITH MULTIPLE COMPONENTS OF THE TRANSCRIPTIONAL PREINITIATION COMPLEX

Simian virus 40 (SV40) large T antigen (Tag) is a promiscuous transcri ptional transactivator; however, its mechanism of transactivation rema ins unknown, Recent studies have suggested the possible involvement of protein-protein interactions with TBP, the TATA box-binding protein o f TFIID, and TEF-1, an enhancer-binding factor. We show here that (i) the Tag domain containing amino acids 133 to 249 directly interacts wi th the general transcription factor TFIIB, the activator protein Spl, 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 eith er at 48 degrees C or with the adenovirus 13S Ela protein; (iv) this d omain of Tag cannot bind concurrently to more than one of these transc ription factors; and (v) the substitution of Tag amino acid residues 1 73 and 174 inactivates the ability of this Tag domain both to associat e with any of these transcription factors and to transactivate the SV4 0 late promoter, Thus, we conclude that SV40 Tag probably does not tra nsactivate 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 f actors that inhibit the formation of preinitiation complexes.