Figure 5.

Simultaneous recruitment of TFIID and TFIIB to a TGTAAA-containing promoter activates transcription synergistically. TFIID is tethered to the promoter by fusing covalently TAF90 to Max–RFX, and TFIIB–Myc is recruited by the same Max–RFX–TAF90 hybrid protein through the Max dimerization domain. TAF90 was also fused at the carboxyl terminus of VP16–RFX to assess activity of VP16 upon artificial recruitment of TFIID. The strains used in these experiments carry a deletion of the TFIIB gene, and they express normal levels of endogenous TAF90 which competes with RFX–TAF90 for its site in the TFIID complex, thus explaining the reduced levels of activation mediated by RFX–TAF90 compared with those observed in Fig. 4.