Practice question

Saccharomyces cerevisiae GAL regulon glucose repression is mediated predominately by C2H2 zinc finger transcription factor Mig1, functional homolog of mammalian EGR proteins. Under high glucose, hexokinase Hxk2 signals inactivation of Snf1 kinase, permitting Mig1 nuclear localization and binding to GC-rich consensus CCCCG motifs in GAL1, GAL4, GAL3 promoters. Mig1 does not mask Gal4 activation domain like Gal80, but actively recruits corepressors to block transcription of structural genes and regulatory activators. Deletion of MIG1 partially relieves glucose repression, allowing galactose-independent GAL expression, demonstrating central role in carbon catabolite repression hierarchy overriding galactose induction signals prioritizing glucose utilization efficiency.