Family of proteins that interact with TFIID and regulate promoter activity.

A family of proteins was shown to bind cooperatively with TFIID to core promoters, as previously demonstrated for the general initiation factor TFIIA. These factors form distinct complexes with TFIID, fail to bind DNA in the absence of TFIID, differ chromatographically from TFIIA, and compete with TFIIA for binding to TFIID. Our results suggest the formation of heterogeneous preinitiation complexes at the step involving TFIIA interactions. This establishes a molecular switch that regulates basal level transcription in vitro and has consequences for transcriptional activation by gene-specific activators.