DROSOPHILA TAF(II)230 AND THE TRANSCRIPTIONAL ACTIVATOR VP16 BIND COMPETITIVELY TO THE TATA BOX-BINDING DOMAIN OF THE TATA BOX-BINDING PROTEIN

The transcription initiation factor TFIID, consisting of the TATA box- binding protein (TBP) and many TBP-associated factors (TAFs), plays a central role in both basal and activated transcription. An intriguing finding is that the 80-residue N-terminal region of Drosophila TAF(II) 230 [dTAF(II)230-(2-81)] can bind directly to TBP and inhibit its func tion, Here, studies with mutated forms of TBP demonstrate that dTAF(II )230-(2-81) binds to the concave surface of TBP, which is important fo r TATA box binding, Previously, it was reported that a point mutation (L114K) on this concave surface destroys the ability of TBP to bind VP 16 and to mediate VP16-dependent activation in vitro, but has no effec t on basal transcription. Importantly the same TBP mutation eliminates TBP binding to dTAF(II)230-(2-81). Consistent with these effects of t he L114K mutation, dTAF(II)230-(2-81) and the VP16 activation domain c ompete for binding to wild-type TBP. These results indicate that trans criptional regulation may involve, in part, competitive interactions b etween transcriptional activators and TAFs on the TBP surface.