Regulation and the role of the sod1+ gene encoding CuZnSOD were investigated in fission yeast Schizosaccharomyces pombe. The amount of sod1+ mRNA decreased in the stationary phase, consistent with the decrease in enzyme activity. The transcript increased by treatment with oxidants such as H(2)O(2) and menadione (MD). Induction by H(2)O(2) was rapid and transient, being dependent on Wis1-Spc1-Atf1 pathway of signal transduction, whereas induction by MD was slow and sustained longer, being independent of Wis1 pathway. Wis1 and Spc1 also turned out to down-regulate sod1+ gene at the stationary phase. Tetrad analysis following sod1+ gene disruption revealed that the sod1Delta cells were not viable, even on rich media. Repression of the sod1+ gene expression by thiamine through nmt1 promoter resulted in the arrest of cell cycle progression following S phase, possibly between G(2) and cytokinesis. The current and previous observations that the viability of Schizosaccharomyces pombe cells, unlike Saccharomyces cerevisiae, critically depends on the action of oxidative defense enzymes in the cytosol, such as CuZnSOD and glutathione reductase, suggest that S. pombe can serve as a good model system to study the effect of oxidative stress on cell proliferation.