INHIBITION OF G(2) M PROGRESSION IN SCHIZOSACCHAROMYCES-POMBE BY A MUTANT CALMODULIN KINASE-II WITH CONSTITUTIVE ACTIVITY/

Intracellular signaling by the second messenger Ca2+ through its recep tor calmodulin (CaM) regulates cell function via the activation of CaM -dependent enzymes. Previous studies have shown that cell cycle progre ssion at G(1)/S and G(2)/M is sensitive to intracellular CaM levels. H owever, little is known about the CaM-regulated enzymes involved. Prot ein phosphorylation has been shown to be important for cell-cycle regu lation. Because CaM regulates several protein kinases, and at least on e protein phosphatase, our studies are focusing on the roles of these enzymes within the cell cycle. As an initial approach to this problem, cDNAs encoding either normal or mutant calcium/calmodulin kinase II ( CaMKII) have been expressed in Schizosaccharomyces pombe. The results show that overexpression of a constitutively active mutant CaMKII caus ed cell-cycle arrest in G(2) Arrest was associated with a failure to a ctivate the p34/cdc2 protein kinase. Expression of the mutant CaMKII i n strains of S. pombe with altered timing of mitosis revealed that thi s effect is not mediated either by cdc25+ or wee1(+), suggesting that CaMKII may regulate G(2)/M progression by another mechanism.