Abstract
The transcriptional activator p53 is known to interact with components of the general transcription factor TFIID in vitro. To examine the relevance of these associations to transcriptional activation in vivo, plasmids expressing a p53-GAL4 chimera and Drosophila TATA-binding protein (dTBP) were transfected into Drosophila Schneider cells. p53-GAL4 and dTBP displayed a markedly synergistic effect on activated transcription from a GAL4 site-containing reporter that was at least 10-fold greater than observed with other activators tested. A mutant p53 previously shown to be defective in both transcriptional activation in vivo and in binding to TBP-associated factors (TAFs) in vitro, although still capable of binding dTBP, did not cooperate with dTBP, suggesting that TAFs may contribute to this synergy. Providing further support for this possibility, transfected dTBP assembled into rapidly sedimenting complexes and could be immunoprecipitated with anti-TAF antibodies. While overexpression of any of several TAFs did not affect basal transcription, in either the presence or the absence of cotransfected dTBP, overexpression of TAFII230 inhibited transcriptional activation mediated by p53-GAL4 as well as by GAL4-VP16 and Sp1. Overexpression of TAFII40 and TAFII60 also inhibited activation by p53-GAL4 but had negligible effects on activation by GAL4-VP16 and Sp1, while TAFII110 did not affect any of the activators. TAF-mediated inhibition of activated transcription could be rescued by high levels of exogenous dTBP, which also restored full synergy. These data demonstrate for the first time that functional interactions can occur in vivo between TBP, TAFs, and p53.
