Activator-mediated disruption of sequence-specific DNA contacts by the general transcription factor TFIIB

The transcription factor TFIIB plays a central role in preinitiation comple x assembly, providing a bridge between promoter-bound TFIID and RNA Polymer ase II. TFIIB possesses sequence-specific DNA-binding ability and interacts with the TFIIB-recognition element (BRE), present in many promoters. Here we show that the BRE suppresses the basal level of transcription elicited b y a core promoter, which increases the amplitude of transcriptional stimula tion in the presence of an activator protein. Further, we find that an acti vator can disrupt the TFIIB-BRE interaction within a promoter-bound complex . Our results reveal a novel function for activators in the modulation of c ore promoter recognition by TFIIB.