Characterization of multicopy suppressor genes that complement a defect in the Wis1-Sty1 MAP kinase cascade involved in stress responses in Schizosaccharomyces pombe

Abstract

The Wis1-Sty1 mitogen-activated protein (MAP) kinase cascade is one of the major signaling systems involved in a wide range of stress responses in Schizosaccharomyces pombe. It is known that Δwis1 and Δsty1 mutants exhibit highly pleiotropic phenotypes, including a phenotype of temperature sensitivity for growth. In this study, we screened multicopy suppressor genes that allow both the Δwis1 and Δsty1 mutants to grow simultaneously at a non-permissive temperature, 37°C. Two such multicopy suppressors were cloned and characterized as sds23+ and hxk2+ genes. The former is known to specify a protein that functions as a multicopy suppressor for mutations of the PP1 protein phosphatase and the 20S cyclosome/anaphase-promoting complex (APC), and the latter encodes hexokinase 2. It was revealed that the multicopy sds23+ gene restored a defect in the mating efficiency caused by the Δwis1 and Δsty1 mutations, whereas the multicopy hxk2+ gene suppressed a phenotype of heat-shock sensitivity for growth of these mutant cells. These findings are discussed with special reference to the Wis1-Sty1 MAP kinase signaling pathway in S. pombe.