Isolation of a fission yeast mutant cell affected in MAP kinase signaling and sterol biosynthesis.

We have previously demonstrated that calcineurin and the Pmk1 MAP kinase pathway play an antagonistic role in Cl-homeostasis. Using this relationship, we screened for mutations that show vic (viable in the presence of immunosuppressant and chloride ion) phenotype and isolated a vic6 mutant cell. The vic6 mutant cells also showed sensitivity to high temperature. Using this phenotype, we isolated hmg1+ gene, encoding a HMG-CoA reductase. Consistently, the vic6 mutant cells exhibited hypersensitivity to miconazole, an inhibitor of ergosterol biosynthesis and showed aberrant intracellular localization of filipin, suggesting that the mutant cells are affected in the sterol biosynthesis. In addition, overexpression of the hmg1+ gene complemented the phenotype of vic1-1/cpp1-v1 mutant cells, an allele of the gene encoding a farnesyltransferase, whereas overexpression of the cpp1+ gene exacerbated the temperature-sensitive phenotype of the vic6 mutant cells.