Structure and Function of a Human [TAF.sub.II]250 Double Bromodomain Module

TFIID is a large multiprotein complex that initiates assembly of the transcription machinery. It is unclear how TFIID recognizes promoters in vivo when templates are nucleosome-bound. Here, it is shown that [TAF.sub.II]250, the largest subunit of TFIID, contains two tandem bromodomain modules that bind selectively to multiply acetylated histone H4 peptides. The 2.1 angstrom crystal structure of the double bromodomain reveals two side-by-side, four-helix bundles with a highly polarized surface charge distribution. Each bundle contains an [N.sup.[Epsilon]]-acetyllysine binding pocket at its center, which results in a structure ideally suited for recognition of diacetylated histone H4 tails. Thus, TFIID may be targeted to specific chromatin-bound promoters and may play a role in chromatin recognition.