Aiba H, Kawaura R, Yamamoto E, Yamada H, Takegawa K, Mizuno T
Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
J Bacteriol. 1998 Oct;180(19):5038-43. doi: 10.1128/JB.180.19.5038-5043.1998.
For the fission yeast Schizosaccharomyces pombe, adaptation to high-osmolarity medium is mediated by a mitogen-activated protein (MAP) kinase cascade, involving the Wis1 MAP kinase kinase and the Sty1 MAP kinase. The MAP kinase pathway transduces an osmotic signal and accordingly regulates the expression of the downstream target gene (gpd1(+)) that encodes NADH-dependent glycerol-3-phosphate dehydrogenase, in order to adaptively accumulate glycerol inside the cells as an osmoprotectant. We previously characterized a set of high-osmolarity-sensitive S. pombe mutants, including wis1, sty1, and gpd1. In this study, we attempted to further isolate novel osmolarity-sensitive mutants. For some of the mutants isolated, profiles of glycerol production in response to the osmolarity of the growth medium were indistinguishable from that of the wild-type cells, suggesting that they are novel types. They were classified into three distinct types genetically and, thus, were designated hos1, hos2, and hos3 (high osmolarity sensitive) mutants. One of them, the hos1 mutant, was characterized in detail. The hos1 mutant was demonstrated to have a mutational lesion in the known ryh1(+) gene, which encodes a small GTP-binding protein. Disruption of the ryh1(+) gene results not only in osmosensitivity but also in temperature sensitivity for growth. It was also found that the delta ryh1 mutant is severely sterile. These results are discussed with special reference to the osmoadaptation of S. pombe.
对于裂殖酵母粟酒裂殖酵母而言，其对高渗培养基的适应性是由丝裂原活化蛋白（MAP）激酶级联反应介导的，该级联反应涉及Wis1 MAP激酶激酶和Sty1 MAP激酶。MAP激酶途径转导渗透信号，并相应地调节下游靶基因（gpd1(+)）的表达，该基因编码依赖于NADH的甘油-3-磷酸脱氢酶，以便在细胞内适应性地积累甘油作为渗透保护剂。我们之前鉴定了一组对高渗敏感的粟酒裂殖酵母突变体，包括wis1、sty1和gpd1。在本研究中，我们试图进一步分离新的对渗透压敏感的突变体。对于一些分离得到的突变体，其甘油产量对生长培养基渗透压的响应曲线与野生型细胞的曲线无法区分，这表明它们是新型突变体。它们在遗传上被分为三种不同类型，因此被命名为hos1、hos2和hos3（高渗敏感）突变体。其中之一，即hos1突变体，被详细表征。已证明hos1突变体在已知的ryh1(+)基因中存在突变损伤，该基因编码一种小GTP结合蛋白。ryh1(+)基因的破坏不仅导致对渗透压敏感，还导致对生长的温度敏感。还发现缺失ryh1的突变体严重不育。将结合粟酒裂殖酵母的渗透适应对这些结果进行讨论。
