Binding of the glucose-dependent Mig1p repressor to the GAL1 and GAL4 promoters in vivo: regulation by glucose and chromatin structure

Binding of the MIG1 repressor to the glucose-repressible GAL1 and GAL4 prom oters was analyzed in vivo by cyclobutane dimer footprinting In two yeast s trains that show different glucose repression responses. Mig1p binding to t he two promoters in both strains was glucose-induced. In cells subject to r apid and stringent glucose repression (S288c), long-term Mig1p binding in g lucose-grown cells was inhibited by the formation of a competing chromatin structure. Under conditions where glucose repression was only partially eff ective (gal80(-) or low glucose), the chromatin structure did not form and long-term Mig1p binding was observed The same long-term binding of Mig1p wa s seen in cells of a different strain (W303A) that shows only partial gluco se repression of the GAL1 promoter. We conclude from these experiments that Mig1p binding to glucose-repressed promoters is glucose-dependent but tran sient. We suggest that Mig1p functions at an early step in repression, but is not required to maintain the repressed state.