SIMIAN-VIRUS-40 LARGE T-ANTIGEN STABILIZES THE TATA-BINDING PROTEIN TFIIA COMPLEX ON THE TATA ELEMENT

Large T antigen (T antigen), the early gene product of simian virus 40 (SV40), is a potent transcriptional activator of both cellular and vi ral genes. Recently we have shown that T antigen is tightly associated with TFIID and, in this position, performs a TATA-binding protein (TB P)-associated factor (TAF)-like function. Based on this observation, w e asked whether T antigen affected steps in preinitiation complex asse mbly. Using purified components in in vitro complex assembly assays, w e found that T antigen specifically enhances the formation of the TBP- TFIIA complex on the TATA element. T antigen accomplishes this by incr easing the rate of formation of the TBP-TFIIA complex on the TATA elem ent and by stabilizing the complexes after they are formed on the prom oter. In addition, DNA immunoprecipitation experiments indicate that T antigen is associated with the stabilized TBP-TFIIA complexes bound t o the DNA. In this regard, it has previously been shown that T antigen interacts with TBP; in the present study, we show that T antigen also interacts with TFIIA in vitro. In testing the ability of T antigen to stabilize the TBP-TFIIA complex, we found that stabilization is highl y sensitive to the specific sequence context of the TATA element. Prev ious studies showed that T antigen could activate simple promoters con taining the TATA elements from the hsp70 and c-fos gene promoters but failed to significantly activate similar promoters containing the TATA elements from the promoters of the SV40 early and adenovirus E2a gene s. We find that the ability to stabilize the TBP-TFIIIA complex on the hsp70 and c-fos TATA elements, and not on the SV40 early and E2A TATA elements, correlates with the ability or inability to activate promot ers containing these TATA elements.