Identification and characterization of a novel gene, hos3(+), the functionof which is necessary for growth under high osmotic stress in fission yeast

hos3 mutants of the fission yeast Schizosaccharomyces pombe showed the phen otype of high osmolarity sensitivity for growth. An S. pombe strain carryin g the hos3-M26 allele cannot form colonies on agar plates containing 2 M gl ucose, but the parental strain can do so very well, as demonstrated previou sly. The hos3(+) gene was cloned and identified as one that encodes a small protein of 94 amino acids, which shows no sequence similarity to any other proteins in the current databases. A hos3 Delta strain, which we then cons tructed, had the phenotype of high osmolarity sensitivity, as in the case o f the original hos3-M26 mutant. More interestingly, when these hos(-) cells were grown in the non-permissive growth condition in the presence of 2 M g lucose, we found that unusually many septated cells were accumulated after a prolonged incubation. A multicopy suppressor gene for hos- mutations was also isolated and identified as the dsk1(+) gene encoding a protein kinase, which was previously suggested to be implicated in a process of the mitoti c regulation of S. pombe. The function of the hos3(+) gene is discussed fro m these results.