Calmodulin and its target enzymes are important regulators of numerous cellular processes, including reversible protein phosphorylation. The calmodulin-dependent protein phosphatase (calcineurin) has been suggested to play roles in activation of T cells and in the mating response of yeast. Recently, studies have shown it to be the target of immunosuppressant drugs such as cyclosporin and FK-506. In this study, we have cloned the gene for the catalytic subunit of calcineurin, CnA, from the yeast Schizosaccharomyces pombe. The gene (named ppb1+) has been mapped to chromosome II by analysis of the hybridization of a genomic DNA probe to an ordered library. The gene produces a single mRNA species of 2.5 kilobases, which varies during the cell cycle in exponentially growing cells. In addition, expression of ppb1+ mRA is induced by nitrogen starvation, a condition that favors mating in S. pombe. The ppb1+ gene promoter contains a cis-acting element for the ste11 transcription factor, and we have shown that induction of the ppb1+ mRNA during nitrogen starvation is dependent on the ste11 gene product. Together with earlier studies showing that disruption of the ppb1+ gene in S. pombe results in sterility (Yoshida, T., Toda, T., and Yanagida, M. (1994) J. Cell Sci., 107, 1725-1735), our studies suggest that the ppb1+ gene plays a role in the gene expression cascade that is essential for mating and sporulation in S. pombe.