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New functions of the SAGA complex in regulation of transcription by RNA polymerase II



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The yeast SAGA (Spt-Ada-Gcn5-acetyltransferase) complex plays a role in Gal4-mediated transcriptional activation via delivery of TATA-binding protein (TBP) to Gal4-responsive promoters. Little is known about the impact of the sequence of the TATA element in the core promoter in this process. To investigate the SAGA complex regulatory function at different TATA element sequences, we compared a consensus element (TATA) to an off-consensus element (CATA) in the kinetics of Gal4-dependent gene activation, PIC occupancy, the requirement of SAGA components, and the histone acetylation state. We have found a new function of SAGA carried by subunits Gcn5, Ada2 and Spt8: TATA-element-censoring. This function enhances transcription driven by the consensus TATA element and represses transcription driven by off-consensus TATA elements. This functions works at both synthetic promoters and the endogenous GAL promoters. Via a genetic screen, Swi/Snf and RSC complexes were also identified with TATA-censoring function. Our study suggests that the new function involves TBP delivery, histone acetylation and histone eviction.
As an important part of transcription, histone eviction involves histone modification, chromatin remodeling and interaction with histone chaperones. We investigated the function of HATs and histone chaperones in GAL gene induction. We found the impacts of deletion of histone chaperones to the transcription of endogenous GAL genes. Also deletions of Nap1 and Asf1 show different change to induction kinetics of GAL1 and GAL7 transcription, which suggests the different functions of these two chaperones and indicates that the histone chaperones at the promoters can affect transcription directly. Our ChIP data on recruitment and post-recruitment promoters show Nap1 occupancy is not related to transcription levels or TBP/RNAPII occupancy. However, Nap1 occupancy has same pattern as SAGA occupancy and the opposite pattern of histone occupancy, suggesting interaction between Nap1, SAGA and histone eviction during galactose induction.


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histone chaperone
RNA polymerase II
SAGA complex
TATA element censoring
TATA element sequence


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