GENOMIC FOOTPRINTING OF MIG1P IN THE MAL62 PROMOTER - BINDING IS DEPENDENT UPON CARBON SOURCE AND COMPETITIVE WITH THE MAL63P ACTIVATOR

Mig1p inhibits gene expression in glucose by binding the Cyc8p (Ssn6p) -Tup1p repressor to the promoter of glucose-repressible genes. While t he binding properties of Mig1p have been studied in vitro and the abil ity of Mig1p-Cyc8p (Ssn6p)-Tup1p to repress has been studied in vivo, no experiments have measured the effect of a carbon source on the in v ivo binding of Mig1p or the effect of bound MIg1p on activator occupan cy of the upstream activation sequence (UAS). To obtain this informati on, we used genomic footprinting to investigate glucose repression of MAL62, a gene that is also regulated by the Mal63p activator. These ex periments show that two interrelated mechanisms are involved in the gl ucose repression of MAL62: 1) competition between the Mal63p activator and Mig1p for DNA binding and 2) modulation of Mig1p binding by the c arbon source. Mig1p affects basal MAL62 expression in the absence of M al63p by binding to a site in the MAL62 promoter and affects Mal63p-de pendent synthesis by also inhibiting the access of Mal63p to site 1 in the UAS(MAL). The binding of Mig1p is increased in glucose and decrea sed in non-repressing sugars, but the increased binding in glucose is not due to an increase in the levels of Mig1p.