In Schizosaccharomyces pombe, Ssp2, an ortholog of AMP-activated protein kinase (AMPK), is critical for cell growth at restrictive temperatures and under glucose depletion as well as sexual differentiation under nitrogen depletion. To identify genes genetically related to Ssp2, we performed a genetic screening to search for the genes whose overexpression rescued the growth defects in Δssp2 cells at restrictive temperatures, and identified 35 cosmids as multicopy suppressor genes. In Southern blot analyses, 22 out of these cosmids were hybridized to an ssp2+ probe. Using nucleotide sequencing, we identified the gsk3+ gene in one of the cosmids, and the remaining 12 cosmids were hybridized to a gsk3+ probe. Overexpression of the gsk3+ gene or the gsk31+ gene, another GSK3 member, rescues defective growth of Δssp2 cells at restrictive temperatures and under glucose depletion as well as sexual differentiation under nitrogen depletion. Δgsk3Δgsk31 double knockout cells, but neither Δgsk3 nor Δgsk31 single knockout cells, phenocopy Δssp2 cells. The deletion of the gsk3+ or gsk31+ gene augments the phenotypes of Δssp2 cells. These findings suggest that Gsk3 and Gsk31 are critical and interact with Ssp2 in multiple cellular functions. 