SYNERGISTIC AND PROMOTER-SELECTIVE ACTIVATION OF TRANSCRIPTION BY RECRUITMENT OF TRANSCRIPTION FACTORS TFIID AND TFIIB

Eukaryotic transcriptional activators map function by stimulating form ation of RNA polymerase II preinitiation complexes at the core promote r of genes, In this case, their mode of action will intrinsically depe nd on how these complexes assemble on promoters in living cells, an is sue that remains largely unexplored, Here we show that in yeast the ba sal transcription machinery is brought to tile promoter in tile form o f at least two subcomplexes, TFIID and a complex comprising TFIIB and other essential components, Individual recruitment of either complex b y artificial contact with a transcriptionally inactive, sequence-speci fic DNA-binding protein suffices to trigger transcriptional activation from a wild-type core promoter bearing the appropriate binding site. In contrast, activation from a promoter containing a weakened TATA ele ment is only observed upon, recruitment of TFIID. Tethering TFIIB on C hat promoter remains without effect, but the simultaneous recruitment of both components leads to strong synergistic activation. These findi ngs suggest a simple mechanism whereby two activators that contact dis tinct subcomplexes of the basal machinery mag stimulate transcription synergistically and differentially depending on the nature of the prom oter.