The hexokinase 2 protein regulates the expression of the GLK1, HXK1 and HXK2 genes of Saccharomyces cerevisiae.
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.
Rodríguez
A
A
Departamento de Bioquímica y Biología Molecular, Instituto Universitario de Biotecnología de Asturias, Universidad de Oviedo, 33006-Oviedo, Spain.
De La Cera
T
T
Herrero
P
P
Moreno
F
F
D004247:DNA / Q000187:drug effects / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D005800:Genes, Fungal / Q000235:genetics*; D005941:Glucokinase / Q000096:biosynthesis / Q000235:genetics*; D005947:Glucose / Q000494:pharmacology; D006593:Hexokinase / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism
D004247:DNA; D006593:Hexokinase; D005941:Glucokinase; D005947:Glucose