Transcriptional repression by Tup1-Ssn6.

The Tup1-Ssn6 complex from budding yeast is one of the best studied corepressors and has served as a model for the study of similar corepressor complexes in higher eukaryotes. Tup1-Ssn6 represses multiple subsets of genes when recruited to promoters by sequence-specific DNA binding repressors. Tup1-Ssn6 mediated repression involves interactions among the corepressor and hypoacetylated histones, histone deacetylases, and the RNA transcriptional machinery. Nucleosome positioning is also involved in repression of a subset of Tup1-Ssn6 regulated genes. These findings highlight the importance of chromatin modification states in Tup1-Ssn6 mediated repression. Here we review the multiple mechanisms involved in repression and discuss Tup1-Ssn6 homolog functions in higher organisms. We also present a model for how repression by Tup1-Ssn6 may be established.