ABSTRACT
Mig1 and Mig2 are proteins with similar zinc fingers that are required for glucose repression of SUC2 expression. Mig1, but not Mig2, is required for repression of some other glucose-repressed genes, including the GAL genes. A second homolog of Mig1, Yer028, appears to be a glucose-dependent transcriptional repressor that binds to the Mig1-binding sites in the SUC2 promoter, but is not involved in glucose repression of SUC2 expression. Despite their functional redundancy, we found several significant differences between Mig1 and Mig2: (1) in the absence of glucose, Mig1, but not Mig2, is inactivated by the Snf1 protein kinase; (2) nuclear localization of Mig1, but not Mig2, is regulated by glucose; (3) expression of MIG1, but not MIG2, is repressed by glucose; and (4) Mig1 and Mig2 bind to similar sites but with different relative affinities. By two approaches, we have identified many genes regulated by Mig1 and Mig2, and confirmed a role for Mig1 and Mig2 in repression of several of them. We found no genes repressed by Yer028. Also, we identified no genes repressed by only Mig1 or Mig2. Thus, Mig1 and Mig2 are redundant glucose repressors of many genes.
Subject(s)
DNA-Binding Proteins/physiology , Gene Expression Regulation, Fungal , Glucose , Glycoside Hydrolases/genetics , Repressor Proteins/physiology , Saccharomyces cerevisiae/genetics , Zinc Fingers , Amino Acid Sequence , Binding Sites , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Genes, Fungal , Molecular Sequence Data , Promoter Regions, Genetic , Repressor Proteins/genetics , Repressor Proteins/metabolism , Saccharomyces cerevisiae/metabolism , Saccharomyces cerevisiae/physiology , Saccharomyces cerevisiae Proteins , Transcription, Genetic , beta-FructofuranosidaseABSTRACT
Expression of the SUC2 gene in Saccharomyces cerevisiae, which encodes invertase, is repressed about 200-fold by high levels of glucose. Mig1p is a Cys2His2 zinc-finger-containing protein required for glucose repression of SUC2 and several other genes. However, SUC2 expression is still about 13-fold repressed by glucose in a mig1 mutant. We have identified a second repressor, Mig2p, containing zinc fingers very similar to those of Mig1p that is responsible for this remaining glucose repression of SUC2 expression. Overexpression of MIG2 represses SUC2 under nonrepressing conditions, and a LexA-Mig2p fusion represses transcription of a lexO-containing promoter in a glucose-dependent manner, supporting the idea that Mig2p is a glucose-activated repressor. We have shown that Mig2p binds to the Miglp-binding sites in the SUC2 promoter. Even though Mig1p and Mig2p bind to similar sites and share almost identical zinc fingers, they differ in their relative affinities for various Mig1p-binding sites. This could explain our observation that MIG2 appears to have little role in glucose repression of other promoters with MIG1-binding sites.
Subject(s)
DNA-Binding Proteins/physiology , Gene Expression Regulation, Fungal/drug effects , Glucose/pharmacology , Glycoside Hydrolases/biosynthesis , Repressor Proteins/physiology , Zinc Fingers/physiology , Amino Acid Sequence , Bacterial Proteins/metabolism , Base Sequence , Binding Sites , Enzyme Induction/drug effects , Glycoside Hydrolases/genetics , Molecular Sequence Data , Promoter Regions, Genetic , Recombinant Fusion Proteins/metabolism , Repressor Proteins/genetics , Saccharomyces cerevisiae Proteins , Sequence Alignment , Sequence Homology, Amino Acid , Serine Endopeptidases/metabolism , beta-FructofuranosidaseABSTRACT
The properties of gene conversion as measured in fungi that generate asci containing all the products of meiosis imply that meiotic recombination initiates at specific sites. The HIS2 gene of Saccharomyces cerevisiae displays a high frequency of gene conversion, indicating that it is a recombination hotspot. The HIS2 gene was cloned and sequenced, and the cloned DNA was used to make several different types of alterations in the yeast chromosome by transformation; these alterations were used to determine the location of the sequences necessary for the high levels of meiotic conversion observed at HIS2. Previous work indicated that the gene conversion polarity gradient is high at the 3' end of the gene, and that the promoter of the gene is not necessary for the high frequency of conversion observed. Data presented here suggest that at least some of the sequences necessary for high levels of conversion at HIS2 are located over 700 bp downstream of the end of the coding region, extend over (at least) several hundred base pairs, and may be quite complex, perhaps involving chromatin structure. Additional data indicate that multiple single base heterologies within a 1-kb interval contribute little to the frequency of gene conversion. This contrasts with other reports about the role of heterologies at the MAT locus.
