title: The Hsp70 homolog Ssb is essential for glucose sensing via the SNF1 kinase network.
abstract: Yeast senses the availability of external energy sources via multiple interconnected signaling networks. One of the central components is SNF1, the homolog of mammalian AMP-activated protein kinase, which in yeast is essential for the expression of glucose-repressed genes. When glucose is available hyperphosphorylated SNF1 is rendered inactive by the type 1 protein phosphatase Glc7. Dephosphorylation requires Reg1, which physically targets Glc7 to SNF1. Here we show that the chaperone Ssb is required to keep SNF1 in the nonphosphorylated state in the presence of glucose. Using a proteome approach we found that the Deltassb1Deltassb2 strain displays alterations in protein expression and suffers from phenotypic characteristics reminiscent of glucose repression mutants. Microarray analysis revealed a correlation between deregulation on the protein and on the transcript level. Supporting studies uncovered that SSB1 was an effective multicopy suppressor of severe growth defects caused by the Deltareg1 mutation. Suppression of Deltareg1 by high levels of Ssb was coupled to a reduction of Snf1 hyperphosphorylation back to the wild-type phosphorylation level. The data are consistent with a model in which Ssb is crucial for efficient regulation within the SNF1 signaling network, thereby allowing an appropriate response to changing glucose levels.
authors.affiliation: Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, D-79104 Freiburg, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: von Plehwe
authors.forename: Uta
authors.initials: U
authors.lastname: Berndt
authors.forename: Charlotte
authors.initials: C
authors.lastname: Conz
authors.forename: Marco
authors.initials: M
authors.lastname: Chiabudini
authors.forename: Edith
authors.initials: E
authors.lastname: Fitzke
authors.forename: Albert
authors.initials: A
authors.lastname: Sickmann
authors.forename: Astrid
authors.initials: A
authors.lastname: Petersen
authors.forename: Dietmar
authors.initials: D
authors.lastname: Pfeifer
authors.forename: Sabine
authors.initials: S
authors.lastname: Rospert
mesh_terms: D015536:Down-Regulation; D015966:Gene Expression Regulation, Fungal; D005947:Glucose / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D054645:Protein Phosphatase 1 / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D018840:HSP70 Heat-Shock Proteins; D029701:Saccharomyces cerevisiae Proteins; C071570:SNF1-related protein kinases; D017346:Protein Serine-Threonine Kinases; D054645:Protein Phosphatase 1; C070829:REG1 protein, S cerevisiae; D005947:Glucose