A TAF4 coactivator function for E proteins that involves enhanced TFIID binding

The multisubunit TFIID plays a direct role in transcription initiation by binding to core promoter elements and directing preinitiation complex assembly. Although TFIID may also function as a coactivator through direct interactions with promoter-bound activators, mechanistic aspects of this poorly defined function remain unclear. Here biochemical studies show a direct TFIID-E protein interaction that (i) is mediated through interaction of a novel E protein activation domain (AD3) with the TAF homology (TAFH) domain of TAF4, (ii) is critical for activation of a natural target gene by an E protein and (iii) mechanistically, acts by enhancing TFIID binding to the core promoter. Complementary assays establish a gene-specific role for the TAFH domain in TFIID recruitment and gene activation in vivo. These results firmly establish TAF4 as a bona fide E protein coactivator, as well as a mechanism involving facilitated TFIID binding through direct interaction with an E protein activation domain. Overall design: Genome-wide profiling of mRNA levels in MEF lines with Taf4 loxp/- (ctrl), Taf4 -/- (ko), Taf4 -/- Tg:hTAF4 wt, and Taf4 -/- Tg: hTAF4 ? (TAFH-deleted).