PMID:11311123

Citation	Rodríguez, A, De La Cera, T, Herrero, P and Moreno, F (2001) The hexokinase 2 protein regulates the expression of the GLK1, HXK1 and HXK2 genes of Saccharomyces cerevisiae. Biochem. J. 355:625-31
Abstract	The key glycolytic HXK2 gene, coding for the enzyme hexokinase 2 (Hxk2p), is expressed when cells of the yeast Saccharomyces cerevisiae are grown on a fermentable medium using glucose, fructose or mannose as a carbon source. After shifting the cells to a non-fermentable carbon source, the HXK2 gene is repressed and the HXK1 and GLK1 genes are rapidly de-repressed, producing the enzymes hexokinase 1 (Hxk1p) and glucokinase (Glk1p) respectively. Because the in vivo functions of the Hxk1p and Glk1p enzymes have remained a mystery so far, we have investigated this glucose-induced regulatory process. Here we demonstrate the involvement of Hxk2p in the glucose-induced repression of the HXK1 and GLK1 genes and the glucose-induced expression of the HXK2 gene. We have also demonstrated the involvement of Hxk1p as a negative factor in the expression of the GLK1 and HXK2 genes. Further experimental evidence, using mutant cells expressing a truncated version of Hxk2p unable to enter the nucleus, shows that nuclear localization of Hxk2p is necessary for glucose-induced repression signalling of the HXK1 and GLK1 genes and for glucose-induced expression of the HXK2 gene. Gel mobility-shift analysis shows that Hxk2p-mediated regulation is exerted through ERA (ethanol repression autoregulation)-like regulatory sequences present in the HXK1 and GLK1 promoters and in two downstream repressing sequences of the HXK2 gene. These findings reveal a novel mechanism of gene regulation whereby the product of a glycolytic gene, normally resident in the cytosol, interacts directly with nuclear proteins to regulate the transcription of the HXK1 and GLK1 genes and to autoregulate its own transcription.
Links	PubMed PMC1221776
Keywords	DNA/drug effects; DNA/metabolism; Gene Expression Regulation, Enzymologic/drug effects; Gene Silencing/drug effects; Genes, Fungal/genetics; Glucokinase/biosynthesis; Glucokinase/genetics; Glucose/pharmacology; Hexokinase/biosynthesis; Hexokinase/genetics; Hexokinase/physiology; Mutation; Saccharomyces cerevisiae/drug effects; Saccharomyces cerevisiae/enzymology; Saccharomyces cerevisiae/genetics; Saccharomyces cerevisiae/metabolism
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