REGULATION OF CALCINEURIN GENE-EXPRESSION IN SCHIZOSACCHAROMYCES-POMBE - DEPENDENCE ON THE STE11 TRANSCRIPTION FACTOR

Calmodulin and its target enzymes are important regulators of numerous cellular processes, including reversible protein phosphorylation. The calmodulin-dependent protein phosphatase (calcineurin) has been sugge sted 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 immunos uppressant drugs such as cyclosporin and FK-506. In this study, we hav e 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 spec ies of 2.5 kilobases, which varies during the cell cycle in exponentia lly growing cells. In addition, expression of ppb1(+) mRA is induced b y nitrogen starvation, a condition that favors mating in S. pombe. The ppb1(+) gene promoter contains a cis-acting element for the ste11 tra nscription factor, and we have shown that induction of the ppb1(+) mRN A during nitrogen starvation is dependent on the ste11 gene product. T ogether with earlier studies showing that disruption of the ppb1(+) ge ne in S. pombe results in sterility (Yoshida, T., Toda, T., and Yanagi da, 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 e ssential for mating and sporulation in S. pombe.