Practice question

Mig1 imposes repression by recruiting general co-repressor complex Cyc8-Tup1, yeast equivalent of metazoan TLE/Groucho corepressors. Mig1 C-terminal repression domain interacts with Tup1 WD40 repeat domain assembled with Cyc8 tetratricopeptide motifs stabilizing tetrameric complex. Assembly subsequently attracts histone deacetylases Rpd3L complex containing Hos2, Hda1, inducing deacetylation of H3K9, H3K18, H4K16 at GAL promoters, increasing nucleosome affinity and masking activation domains. Deacetylation reduces accessibility for acetyltransferase Gcn5 within SAGA complex, preventing Gal4 contacting basal machinery despite enhancer occupancy. Tup1-HDAC activity regulates approximately 300 glucose-repressed genes, illustrating leverage of sequence-specific repressor using conserved co-repressor hub mediating metabolic adaptation.