Differential Requirement of SAGA Subunits for Mot1p and Taf1p Recruitment in Gene Activation

Abstract

Transcription activation in yeast (Saccharomyces cerevisiae) involves ordered recruitment of transcription factor complexes, such as TFIID, SAGA, and Mot1p. Previously, we showed that both Mot1p and Taf1p are recruited to the HXT2 and HXT4 genes, which encode hexose transporter proteins. Here, we show that SAGA also binds to the HXT2 and HXT4 promoters and plays a pivotal role in the recruitment of Mot1p and Taf1p. The deletion of either SPT3 or SPT8 reduces Mot1p binding to HXT2 and HXT4. Surprisingly, the deletion of GCN5 reduces Taf1p binding to both promoters. When GCN5 is deleted in spt3⌬ or spt8⌬ strains, neither Mot1p nor Taf1p binds, and this results in a diminished recruitment of TATA binding protein and polymerase II to the HXT4 but not the HXT2 promoter. This is reflected by the SAGA-dependent expression of HXT4. In contrast, SAGA-independent induction of HXT2 suggests a functional redundancy with other factors. A functional interplay of different SAGA subunits with Mot1p and Taf1p was supported by phenotypic analysis of MOT1 SAGA or TAF1/SAGA double mutant strains, which revealed novel genetic interactions between MOT1 and SPT8 and between TAF1 and GCN5. In conclusion, our data demonstrate functional links between SAGA, Mot1p, and TFIID in HXT gene regulation.

Characterization of New Spt3 and TATA-Binding Protein Mutants of Saccharomyces cerevisiae: Spt3–TBP Allele-Specific Interactions and Bypass of Spt8

“…We cannot rule out other models in which Spt3 and TBP interact indirectly by altered interactions with other proteins, such as those in SAGA or other general transcription factors. For example, evidence exists for functional interactions of Spt3 with Mot1 (Collart 1996;Madison and Winston 1997;Topalidou et al 2004;Van Oevelen et al 2005). Such a model does not easily explain the allele specificity that has been demonstrated between spt3 and spt15 mutations, however, including at the level of TBP recruitment (this work and Larschan and Winston 2001).…”

“…The factors that determine positive vs. negative regulation by Spt3 and Spt8 are not currently understood, although the factors Swi/Snf or yFACT may play a role (Biswas 1 et al 2005;Mitra et al 2006). In addition to controlling the level of TBP-TATA interaction, Spt3 and Spt8 have been implicated in recruiting Mot1 to activate transcription by a mechanism independent of TBP recruitment (Topalidou et al 2004;Van Oevelen et al 2005). A recent study also suggests a role for Spt3 outside of SAGA ( James et al 2007).…”

Snf1p-dependent Spt-Ada-Gcn5-acetyltransferase (SAGA) Recruitment and Chromatin Remodeling Activities on the HXT2 and HXT4 Promoters

“…Although the SAGA complex is required for the recruitment of both Mot1p and the TFIID subunit, Taf1p, to the TATA box regions via different modules, SAGA is only essential for HXT4 expression (40). Here, we describe a functional link between release of repression by Snf1p, SAGA recruitment, and its consequences for chromatin regulation of the HXT2 and HXT4 promoters.…”

“…We have shown recently that SAGA is specifically recruited to the upstream regions of the HXT2 and HXT4 genes (40). Although the SAGA complex is required for the recruitment of both Mot1p and the TFIID subunit, Taf1p, to the TATA box regions via different modules, SAGA is only essential for HXT4 expression (40).…”

Genetic Interactions Between Nhp6 and Gcn5 With Mot1 and the Ccr4–Not Complex That Regulate Binding of TATA-Binding Protein in Saccharomyces cerevisiae

“…As shown in Figure 8A, there is decreased TBP binding to the RPS5, HXT4, SER3, and URA1 promoters in the nhp6, gcn5, and mot1(R1243I) mutants. Other mot1 mutations have previously been shown to affect TBP binding to HXT4 and URA1 (Dasgupta et al 2005;van Oevelen et al 2005). Importantly, not all promoters are affected so strongly, for example, ELP3.…”