YEAST HAS HOMOLOGS (CNA1 AND CNA2 GENE-PRODUCTS) OF MAMMALIAN CALCINEURIN, A CALMODULIN-REGULATED PHOSPHOPROTEIN PHOSPHATASE

Calcineurin, or phosphoprotein phosphatase type 2B (PP2B), is a calmodulin-regulated phosphoprotein phosphatase. We isolated a gene encoding a yeast PP2B homolog (CNA1) by screening a yeast genomic DNA library in the expression vector lambda-gt11, first with I-125-labeled yeast calmodulin and then with a human cDNA encoding the catalytic (or A) subunit of calcineurin. The predicted CNA1 gene product is 54% identical to its mammalian counterpart. Using the polymerase chain reaction (PCR) with oligonucleotide primers based on sequences conserved between CNA1 and mammalian PP2B genes, we isolated a second gene, CNA2. CNA2 is identical to PP2B(w), a partial cDNA clone previously described by others as originating from rabbit brain tissue. Our findings demonstrate that a unicellular eukaryote contains phosphoprotein phosphatases of the 2B class. Haploid cells containing a single cna1 or cna2 null mutation, or both mutations, were viable. MATa cna1 cna2 double mutants were more sensitive than wild-type cells or either single mutant to growth arrest induced by the mating pheromone alpha-factor and failed to resume growth during continuous exposure to alpha-factor. Thus, calcineurin action antagonizes the mating-pheromone response pathway.