title: Characterization of the osmotic-stress response in Saccharomyces cerevisiae: osmotic stress and glucose repression regulate glycerol-3-phosphate dehydrogenase independently.
abstract: Micro-organisms have developed systems to adapt to sudden changes in the environment. Here we describe the response of the yeast Saccharomyces cerevisiae to osmotic stress. A drop in the water activity (aw) of the medium following the addition of NaCl led to an immediate shrinkage of the cells. During the 2 h following the osmotic shock the cells partially restored their cell volume. This process depended on active protein synthesis. During the recovery period the cells accumulated glycerol intracellularly as a compatible solute and very little glycerol was leaking out of the cell. We have investigated in more detail the enzymes of glycerol metabolism and found that only the cytoplasmic glycerol-3-phosphate dehydrogenase was strongly induced. The level of induction was dependent on the yeast strain used and the degree of osmotic stress. The synthesis of cytoplasmic glycerol-3-phosphate dehydrogenase is also regulated by glucose repression. Using mutants defective in glucose repression (hxk2 delta), or derepression (snf1 delta), and with invertase as a marker enzyme, we show that glucose repression and the osmotic-stress response system regulate glycerol-3-phosphate dehydrogenase synthesis independently. We infer that specific control mechanisms sense the osmotic situation of the cell and induce responses such as the production and retention of glycerol.
authors.affiliation: Department of Microbiology and Biochemistry, University of the Orange Free State, Bloemfontein, South Africa.
authors.forename: J
authors.initials: J
authors.lastname: Albertyn
authors.forename: S
authors.initials: S
authors.lastname: Hohmann
authors.forename: B A
authors.initials: BA
authors.lastname: Prior
mesh_terms: D004790:Enzyme Induction; D005800:Genes, Fungal; D005947:Glucose / Q000494:pharmacology; D005990:Glycerol / Q000378:metabolism; D005993:Glycerolphosphate Dehydrogenase / Q000096:biosynthesis* / Q000235:genetics; D009154:Mutation; D009997:Osmotic Pressure; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D005993:Glycerolphosphate Dehydrogenase; D005947:Glucose; D005990:Glycerol