Studies on the regulatory mechanisms of TFIID-mediated eukaryotic transcription

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Saccharomyces cerevisiae HM01, a high mobility group B (HMGB) protein, associates with the rRNA locus and with the promoters of many ribosomal protein genes (RPGs) .Here, the Sos recruitment system was used to show that HM01 interacts with TBP and the N-terminal domain (TAND) of TAF1, which are integral components of TFIID. Biochemical studies revealed that HM01 copurifies with TFIID and directly interacts with TBP but not with TAND. Deletion of HM01 (Deltahmol) causes a severe cold-sensitive growth defect and decreases transcription of some TAND-dependent genes. Deltahmol also affects TFIID occupancy at some RPG promoters in a promoter-specific manner. Interestingly, over-expression of HM01 delays colony formation of tafl mutants lacking TAND (taf1DeltaTAND), but not of the wild-type strain, indicating a functional link between HM01 and TAND. Furthermore, Deltahmol exhibits synthetic growth defects in some spt15 (TBP) and toal (TFIIA) mutants while it rescues growth defects of some su … More a7 (TFIIB) mutants. Importantly, Deltahmol causes an upstream shift in transcriptional start sites of RPS5, RPS16A, RPL23B, RPL27B and RPL32, but not of RPS31, RPL10, TEF2 and ADH1, indicating that HM01 may participate in start site selection of a subset of class II genes presumably via its interaction with TFIID.This study also uses genome-wide chromatin immunoprecipitation to study the roles of HMO1, FHL1, and RAP1 in RPG transcription. The results show that RPG promoters(138 in total) can be classified into several distinct groups based on HM01 abundance at the promoter and the HM01 dependence of FHL1 and/or RAP1 binding to the promoter. FHL1 binds to most of the HMO1-enriched and transcriptionally HMO1-dependent RPG promoters in an HMO1-dependent manner, whereas it binds to HMO1-limited RPG promoters in an HMO1-independent manner, irrespective of whether they are transcribed in an HMO1-dependent manner. Importantly, these functional properties are determined by the promoter sequence. Less