TAF-LIKE FUNCTION OF SV40 LARGE T-ANTIGEN

The simian virus 40 (SV40) early gene product large T antigen promiscu ously activates simple promoters containing a TATA box or initiator el ement and at least one upstream transcription factor-binding site. Pre vious studies have suggested that promoter activation requires that la rge T antigen interacts with both the basal transcription complex and the upstream-bound factor. This mechanism of activation is similar to that proposed for TBP-associated factors (TAFs). We report genetic and biochemical evidence suggesting that large T antigen performs a TAF-l ike function. In the ts13 cell line, large T antigen can rescue the te mperature-sensitive (ts) defect in TAF(II)250. In contrast, neither El a, small t antigen, nor mutants of large T antigen defective in transc riptional activation were able to rescue the ts defect. These data sug gest that transcriptional activation by large T antigen is attributabl e, at least in part, to an ability to augment or replace a function of TAF,,250. In addition, we show that large T antigen interacts in vitr o with the Drosophila TAFs (dTAFs) dTAF(II)150, dTAF(II)110, and dTAF( II)40, as well as TBP. The relevance of these in vitro results was est ablished in coimmunoprecipitation experiments using extracts of SV40-i nfected alpha 3 cells that express an epitope-tagged TBP. Large T anti gen was coimmunoprecipitated by antibodies to epitope-tagged TBP, endo genous TBP, hTAF(II)100, hTAF(II)130, and hTAF(II)250, under condition s where holo-TFIID would be precipitated. In addition, large T antigen copurified and coimmunoprecipitated with phosphocellulose- purified T FIID from SV40-infected alpha 3 cells. Large T antigen also coprecipit ated with anti-TBP antibody from extracts of ts13 cells expressing wil d-type large T antigen under conditions where the ts defect in TAF(II) 250 was rescued. In contrast, a trans-activation mutant of large T ant igen, which was unable to rescue the ts defect, failed to coprecipitat e. We conclude from these data that transcriptional activation of many promoters by large T antigen results from its performing a TAF-like f unction in a complex with TFIID.