Glucose repression of the MAL genes in the yeast Saccharomyces cerevisiae
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The metabolism of maltose in the yeast Saccharomyces cerevisiae requires one of five unlinked MAL loci. Each MAL locus contains three genes, MALS, encoding maltase, MALT, encoding maltose permease and MALR, encoding the MAL regulatory protein. MALT and MALS are coordinately regulated by maltose induction and glucose repression.;The mechanism of glucose repression of the MAL genes was studied by biochemical and genetic analysis. The cis-acting elements involved in maltose induction and glucose repression were studied by promoter deletions and reporter gene fusions. Factors involved in glucose repression of the MAL genes were studied by extensive mutant screening, gene cloning and subsequent characterization of the cloned genes. Comparisons between the glucose repression of the MAL genes and the GAL genes were carried out using yeast constructs that allowed the expression of both gene families to be monitored simultaneously in an identical genetic background. The interactions between maltose induction and glucose repression were studied by the yeast two-hybrid system, in vivo footprinting and gene overexpression. Based on these studies, it was concluded that the expression of the MAL structural genes is determined by a competition between general transcriptional repressors and gene specific activators. A model is proposed that integrates maltose induction and glucose repression in the regulation of MAL gene expression.