Glucose repression is a global regulatory mechanism in yeast. We have investigated how glucose regulates the GAL genes, which are required for galactose fermentation. We found that the GAL genes are controlled by a transcriptional cascade. Thus, GAL4, which encodes an activator of the GAL genes, is repressed by MIG1, a zinc finger protein that binds to the GAL4 promoter. MIG1 has a dual role in control of the GAL genes, since MIG1 also binds to the promoter of GAL1, a gene regulated by GAL4. A disruption of MIG1 interacts synergistically with a disruption of GAL80, a gene involved in galactose induction. This suggests that the MIG1-dependent response to glucose is amplified by down-regulation of the induction pathway.