title: Engineering of the yeast ubiquitin ligase Rsp5: isolation of a new variant that induces constitutive inactivation of the general amino acid permease Gap1.
abstract: Rsp5 is an essential ubiquitin-protein ligase in Saccharomyces cerevisiae. We found previously that the Ala401Glu rsp5 mutant is hypersensitive to various stresses that induce protein misfolding, suggesting that Rsp5 is a key enzyme for yeast cell growth under stress conditions. To isolate new Rsp5 variants as suppressors of the A401E mutant, PCR random mutagenesis was used in the rsp5(A401E) gene, and the mutagenized plasmid library was introduced into rsp5(A401E) cells. As a phenotypic suppressor of rsp5(A401E) cells, we isolated a quadruple variant (Thr357Ala/Glu401Gly/Lys764Glu/Glu767Gly) on a minimal medium containing the toxic proline analogue azetidine-2-carboxylate (AZC). Site-directed mutagenesis experiments showed that the rsp5(T357A/K764E) cells were much more tolerant to AZC than the wild-type cells, due to the smaller amounts of intracellular AZC. However, the T357A/K764E variant Rsp5 did not reverse the hypersensitivity of rsp5(A401E) cells to other stresses such as high growth temperature, ethanol, and freezing treatment. Interestingly, immunoblot and localization analyses indicated that the general amino acid permease Gap1, which is involved in AZC uptake, was absent on the plasma membrane and degraded in the vacuole of rsp5(T357A/K764E) cells before the addition of ammonium ions. These results suggest that the T357A/K764E variant Rsp5 induces constitutive inactivation of Gap1.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Haitani
authors.forename: Maiko
authors.initials: M
authors.lastname: Nakata
authors.forename: Toshiya
authors.initials: T
authors.lastname: Sasaki
authors.forename: Akiko
authors.initials: A
authors.lastname: Uchida
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takagi
mesh_terms: D026905:Amino Acid Transport Systems / Q000037:antagonists & inhibitors*; D000935:Antifungal Agents / Q000494:pharmacology; D001383:Azetidinecarboxylic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D025141:Drug Resistance, Fungal; D056827:Endosomal Sorting Complexes Required for Transport; D005816:Genetic Complementation Test; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics* / Q000378:metabolism*; D020125:Mutation, Missense; D016133:Polymerase Chain Reaction / Q000379:methods; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics* / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000235:genetics* / Q000378:metabolism*
chemical_list: D026905:Amino Acid Transport Systems; D000935:Antifungal Agents; D056827:Endosomal Sorting Complexes Required for Transport; C491145:GAP1 protein, S cerevisiae; D050505:Mutant Proteins; D029701:Saccharomyces cerevisiae Proteins; C083095:azetidine-2,4-dicarboxylic acid; D001383:Azetidinecarboxylic Acid; D043743:Ubiquitin-Protein Ligase Complexes; C469287:RSP5 protein, S cerevisiae