Tup1p represses Mcm1p transcriptional activation and chromatin remodeling of an a-cell-specific gene

In yeast, a number of regulatory proteins expressed only in specific cell t ypes interact with general transcription factors in a combinatorial manner to control expression of cell-type-specific genes. We report a detailed ana lysis of activation and repression events that occur at the promoter of the a-cell-specific STE6 gene fused to a beta -galactosidase gene in a yeast m inichromosome, as well as factors that control the chromatin structure of t his promoter both in the minichromosome and in the genomic STE6 locus. Mcm1 p results in chromatin remodeling and is responsible for all transcriptiona l activity from the STE6 promoter in both wild-type a and alpha cells. Mat alpha 2p cooperates with Tup1p to block both chromatin remodeling and Mcm1p -associated activation. While Mata2p represses only Mcm1p, the Tup1p-mediat ed repression involves both Mcm1p-dependent and -independent mechanisms, Sw i/Snf and Gcn5p, required for full induction of the STE6 gene, do not contr ibute to chromatin remodeling. We suggest that Tup1p can contribute to repr ession by blocking transcriptional activators, in addition to interacting w ith transcription machinery and stabilizing chromatin.