Identification and characterization of a novel gene, hos2(+), the functionof which is necessary for growth under high osmotic stress in fission yeast

hos2 mutants of the fission yeast Schizosaccharomyces pombe showed the phen otype of high osmolarity sensitivity for growth. An S. pombe strain carryin g the hos2-M10 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. In this study, the hos2(+) gene was identified as one that encodes a s mall protein of 94 amino acids, which shows no sequence similarity to any o ther proteins in the current databases. The hod-MIO mutation resulted in Gl n-62 to TAG-termination codon. A Hos2-defective (hos2 Delta) strain, which we then constructed, showed the phenotype of high osmolarity sensitivity, a s in the case of the original hos2-M10 mutant. For this hos2 Delta mutant, three multicopy suppressor genes were isolated and one of which was identif ied as the pgk1(+) gene, encoding a phosphoglycerate kinase.