Distinct TPR motifs of Cyc8 are involved in recruiting the Cyc8-Tup1 corepressor complex to differentially regulated promoters.

The yeast Cyc8(Ssn6)-Tup1 complex is required for transcriptional repression of distinct sets of genes that are regulated by glucose, oxygen, cell type, and DNA damage. It has been proposed that the Cyc8-Tup1 complex is a corepressor that is recruited to promoters by interacting with pathway-specific DNA-binding proteins. Previously, we showed that a specific region of Tup1 mediates the general transcriptional repression function of the complex. Here, we define functional domains of Cyc8, a protein consisting primarily of 10 tandem copies of a TPR motif. Distinct combinations of TPR motifs are required specifically for direct interaction with Tup1, repression of oxygen-regulated genes, and repression of glucose-regulated genes. In contrast, the WD motifs of Tup1 are not essential for repression of genes regulated by glucose and oxygen, but they are required for those regulated by cell type and DNA damage. In addition, we show that the Cyc8-Tup1 complex functions both as a corepressor and an inhibitor of Mig1, a protein that binds to promoters of glucose-repressible genes. These observations suggest that different Cyc8 TPR motifs and the Tup1 WD domain mediate distinct protein-protein interactions that link the Cyc8-Tup1 corepressor to structurally dissimilar DNA-binding proteins required for pathway-specific regulation.