title: Galactose induction of the GAL1 gene requires conditional degradation of the Mig2 repressor.
abstract: Skp1 an essential component of the SCF (Skp1/cullin/F-box) E3 ubiquitin ligases, which target proteins for degradation by the 26S proteasome. We generated a skp1dM mutant strain that is defective for galactose induction of the GAL1 gene and we have found that galactose-induced protein degradation of the repressor Mig2 is defective in this strain. Mig2 degradation was also abolished in cells lacking the protein kinase Snf1 and the F-box protein Das1, suggesting that Snf1 triggers galactose-induced protein degradation of Mig2 by SCFDas1. Chromatin immunoprecipitation showed that Mig2 associates with the GAL1 promoter upon the galactose-induced exit of Mig1 in skp1dM cells, but not in wild-type cells, suggesting that the conditional degradation of Mig2 is required to prevent it from binding to the GAL1 promoter under inducing conditions. A galactose-stable deletion derivative of Mig2 caused a strong Mig (multi-copy inhibition of GAL gene expression) phenotype, confirming that galactose induction of the GAL1 gene requires the degradation of the repressor Mig2. Our results shed new light on the conflicting reports about the functional role of the degradation of transcriptional activators and indicate that gene expression studies interfering with proteasome degradation should take the stabilization of potential repressors into account.
authors.affiliation: Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, 5 Science Drive 2, Block MD4, Singapore 117597.
authors.forename: Mei Kee
authors.initials: MK
authors.lastname: Lim
authors.forename: Wee Leng
authors.initials: WL
authors.lastname: Siew
authors.forename: Jin
authors.initials: J
authors.lastname: Zhao
authors.forename: Ywee Chieh
authors.initials: YC
authors.lastname: Tay
authors.forename: Edwin
authors.initials: E
authors.lastname: Ang
authors.forename: Norbert
authors.initials: N
authors.lastname: Lehming
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism; D005686:Galactokinase / Q000235:genetics / Q000378:metabolism*; D005690:Galactose / Q000494:pharmacology*; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects*; D009154:Mutation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C465210:Act1 protein, S cerevisiae; D000199:Actins; C539385:Mig2 protein, S cerevisiae; D012331:RNA, Fungal; D012333:RNA, Messenger; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C524219:GAL1 protein, S cerevisiae; D005686:Galactokinase; D005690:Galactose