title: Novel alleles of yeast hexokinase PII with distinct effects on catalytic activity and catabolite repression of SUC2.
abstract: In the yeast Saccharomyces cerevisiae, glucose or fructose represses the expression of a large number of genes. The phosphorylation of glucose or fructose is catalysed by hexokinase PI (Hxk1), hexokinase PII (Hxk2) and a specific glucokinase (Glk1). The authors have shown previously that either Hxk1 or Hxk2 is sufficient for a rapid, sugar-induced disappearance of catabolite-repressible mRNAs (short-term catabolite repression). Hxk2 is specifically required and sufficient for long-term glucose repression and either Hxk1 or Hxk2 is sufficient for long-term repression by fructose. Mutants lacking the TPS1 gene, which encodes trehalose 6-phosphate synthase, can not grow on glucose or fructose. In this study, suppressor mutations of the growth defect of a tps1delta hxk1delta double mutant on fructose were isolated and identified as novel HXK2 alleles. All six alleles studied have single amino acid substitutions. The mutations affected glucose and fructose phosphorylation to a different extent, indicating that Hxk2 binds glucose and fructose via distinct mechanisms. The mutations conferred different effects on long- and short-term repression. Two of the mutants showed very similar defects in catabolite repression, despite large differences in residual sugar-phosphorylation activity. The data show that the long- and short-term phases of catabolite repression can be dissected using different hexokinase mutations. The lack of correlation between in vitro catalytic hexokinase activity, in vivo sugar phosphate accumulation and the establishment of catabolite repression suggests that the production of sugar phosphate is not the sole role of hexokinase in repression. Using the set of six hxk2 mutants it was shown that there is a good correlation between the glucose-induced cAMP signal and in vivo hexokinase activity. There was no correlation between the cAMP signal and the short- or long-term repression of SUC2, arguing against an involvement of cAMP in either stage of catabolite repression.
authors.affiliation: Department of Cell and Molecular Biology/Microbiology, Göteborg University, Box 462, S-40530 Göteborg, Sweden.|Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Flanders, Belgium.
authors.forename: Stefan
authors.initials: S
authors.lastname: Hohmann
authors.affiliation: Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Flanders, Belgium.
authors.forename: Joris
authors.initials: J
authors.lastname: Winderickx
authors.affiliation: Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Flanders, Belgium.
authors.forename: Johannes H
authors.initials: JH
authors.lastname: de Winde
authors.affiliation: Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Flanders, Belgium.
authors.forename: Dirk
authors.initials: D
authors.lastname: Valckx
authors.affiliation: Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Flanders, Belgium.
authors.forename: Philip
authors.initials: P
authors.lastname: Cobbaert
authors.affiliation: Departamento de Microbiologia, ETSIAM, Universidad de Cordóba, E-14080 Cordóba, Spain.|Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Flanders, Belgium.
authors.forename: Kattie
authors.initials: K
authors.lastname: Luyten
authors.affiliation: Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Flanders, Belgium.
authors.forename: Catherine
authors.initials: C
authors.lastname: de Meirsman
authors.affiliation: Departamento de Microbiologia, ETSIAM, Universidad de Cordóba, E-14080 Cordóba, Spain.
authors.forename: José
authors.initials: J
authors.lastname: Ramos
authors.affiliation: Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Flanders, Belgium.
authors.forename: Johan M
authors.initials: JM
authors.lastname: Thevelein
mesh_terms: D000483:Alleles; D000242:Cyclic AMP / Q000378:metabolism; D004794:Enzyme Repression; D005632:Fructose / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D005947:Glucose / Q000378:metabolism; D005964:Glucosyltransferases / Q000235:genetics; D006019:Glycolysis; D006026:Glycoside Hydrolases / Q000096:biosynthesis* / Q000378:metabolism; D006593:Hexokinase / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D015398:Signal Transduction; D013379:Substrate Specificity; D013489:Suppression, Genetic; D043324:beta-Fructofuranosidase
chemical_list: D005632:Fructose; D000242:Cyclic AMP; D005964:Glucosyltransferases; C023180:trehalose-6-phosphate synthase; D006593:Hexokinase; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase; D005947:Glucose