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 spt3Δ or spt8Δ 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.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/.

ACKNOWLEDGMENTS

We are grateful to members of the Timmers laboratory for helpful discussions and technical advice. We thank F. Holstege and P. Pijnappel for providing 12CA5 monoclonal antibody. We also thank J.-C. Andrau for providing yeast strains, P. A. Weil for providing anti-TBP antibodies and yeast strains, G. Thireos for supplying the GCN5 disruption cassette, and J. Thorner for sharing unpublished information.

H.T.M.T. and C.J.C.V.O. were supported by grants from The Netherlands Organization for Scientific Research (NWO-MW Pionier 900-98-142) and the European Union (Improving Human Potential RTN2-2001-00026).