Osmoregulation and signal transduction of fission yeast.

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Many types of microorganisms, including both prokaryoutes and eukaryoutes, have developed mechanisms to adapt severe osmotic stress. Although a large number of physiological phenomena correlated to the osumoregulation have been described for many microorganisms, very little was known about its genetic and molecular basis. We thus began to study the mechanism of osumoregulation in Schizosaccharomyces pombe. For the first step, we isolated several kinds of osmosensitive mutants. Then we identified multicoy supresser genes for those mutants. Tow genes (named gpd1 and gpd2), which encode an isozyme of NADH-dependent glycerol-3-phosphate dehydrogenase (GPD) that is involved in glycerol synthesis were isolated. We showed that the gpd1 and gpd2 gene-products are both functional in terms of the de novo glycerol synthesis. Furthermare, the gpd1-mediated glycerol production is primarily responsible for the osumoregulation, but the gpd2 gene is not. Interestingly, however, the gpd2 deletion mutant had histidine-or lysine-auxotrophy for growth on a minimal medium. We showed that expression of gpd1 is osmoregulated at the level of transcription. We clarified the structure of the osmoinducible promoter of the gpd1. We also provide evidence that this osmotic induction of gpd1 is under the control of the Wisl MAP (mitogen-activated protein) kinase pathway.