Artificially recruited TATA-binding protein fails to remodel chromatin anddoes not activate three promoters that require chromatin remodeling

Transcriptional activators are believed to work in part by recruiting gener al transcription factors, such as TATA-binding protein (TBP) and the RNA po lymerase II holoenzyme. Activation domains also contribute to remodeling of chromatin in vivo. To determine whether these two activities represent dis tinct functions of activation domains, we have examined transcriptional act ivation and chromatin remodeling accompanying artificial recruitment of TBP in yeast (Saccharomyces cerevisiae), We measured transcription of reporter genes with defined chromatin structure by artificial recruitment of TBP an d found that a reporter gene whose TATA element was relatively accessible c ould be activated by artificially recruited TBP, whereas two promoters, GAL 10 and CHA1, that have accessible activator binding sites, but nucleosomal TATA elements, could not. A third reporter gene containing the HIS4 promote r could be activated by GAL4-TBP only when a RAP1 binding site was present, although RAP1 alone could not activate the reporter, suggesting that RAP1 was needed to open the chromatin structure to allow activation. Consistent with this interpretation, artificially recruited TBP was unable to perturb nucleosome positioning via a nucleosomal binding site, in contrast to a tru e activator such as GAL4, or to perturb the TATA-containing nucleosome at t he CHA1 promoter. Finally, we show that activation of the GAL10 promoter by GAL4, which requires chromatin remodeling, can occur even in swi gcn5 yeas t, implying that remodeling pathways independent of GCN5, the SWI-SNF compl ex, and TFIID can operate during transcriptional activation in vivo.