Fission yeast Pom1p kinase activity is cell cycle regulated and essential for cellular symmetry during growth and division

Schizosaccharomyces pombe cells grow from both ends during most of interpha se and divide symmetrically into two daughter cells. The pom1 gene, encodin g a member of the Dyrk family of protein kinases, has been identified throu gh a mutant showing abnormal cellular morphogenesis. Here we show that Pom1 p kinase activity is cell cycle regulated in correlation,vith the state of cellular symmetry: the activity is high during symmetrical growth and divis ion, but lower when cells grow at just one end. Point mutations in the cata lytic domain lead to asymmetry during both cell growth and division, whilst cells overexpressing Pom1p form additional growing ends. Manipulations of kinase activity indicate a negative role for Pom1p in microtubule growth at cell ends. Pom1p is present in a large protein complex and requires its no n-catalytic domain to localize to the cell periphery and its kinase activit y to localize to cell ends. These data establish that Pom1p kinase activity plays an important role in generating cellular symmetry and suggest that t here may be related roles of homologous protein kinases ubiquitously presen t in all eukaryotes.