TFIID is a multimeric protein complex that plays a central role in mediating promoter responses to various activators and repressors. May function as a coactivator by serving as a site of protein-protein contact between activators like Sp1 (or btd) and TFIID complex. Belongs to the TFIID complex which is composed of TATA binding protein (Tbp) and a number of TBP-associated factors (TAFs). Interacts with TFIIA-L when in complex with Tbp. Interacts with Taf1, Taf5, Taf11 and Taf12. Belongs to the TAF4 family.