title: Regulatory mutations of inositol biosynthesis in yeast: isolation of inositol-excreting mutants.
abstract: The enzyme inositol-1-phosphate synthase (I-1-P synthase), product of the INO1 locus, catalyzes the synthesis of inositol-1-phosphate from the substrate glucose-6-phosphate. The activity of this enzyme is dramatically repressed in the presence of inositol. By selecting for mutants which overproduce and excrete inositol, we have identified mutants constitutive for inositol-1-phosphate synthase as well as a mutation in phospholipid biosynthesis. Genetic analysis of the mutants indicates that at least three loci (designated OPI1, OPI2 and OPI4) direct inositol-mediated repression of I-1-P synthase. Mutants of these loci synthesize I-1-P synthase constitutively. Three loci are unlinked to each other and to INO1, the structural gene for the enzyme. A mutant of a fourth locus, OPI3, does not synthesize I-1-P synthase constitutively, despite its inositol excretion phenotype. This mutant is preliminarily identified as having a defect in phospholipid synthesis.
mesh_terms: D005799:Genes, Dominant; D005808:Genes, Recessive; D005809:Genes, Regulator; D007294:Inositol / Q000378:metabolism*; D008563:Membrane Lipids / Q000378:metabolism; D009154:Mutation; D007296:Myo-Inositol-1-Phosphate Synthase / Q000235:genetics; D010743:Phospholipids / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism
chemical_list: D008563:Membrane Lipids; D010743:Phospholipids; D007294:Inositol; D007296:Myo-Inositol-1-Phosphate Synthase