POM1P, A FISSION YEAST PROTEIN-KINASE THAT PROVIDES POSITIONAL INFORMATION FOR BOTH POLARIZED GROWTH AND CYTOKINESIS

Schizosaccharomyces pombe cells have a well-defined pattern of polariz ed growth at the cell ends during interphase and divide symmetrically into two equal-sized daughter cells. We identified a gene, pom1, that provides positional information for both growth and division in S. pom be. pom1 mutants form functioning growth zones and division septa but show several abnormalities: (1) After division, cells initiate growth with equal frequencies from either the old or the new end; (2) most ce lls never switch to bipolar growth but instead grow exclusively at the randomly chosen end; (3) some cells mislocalize their growth axis alt ogether, leading to the formation of angled and branched cells; and (4 ) many cells misplace and/or misorient their septa, leading to asymmet ric cell division, pom1 encodes a putative protein kinase that is conc entrated at the new cell end during interphase, at both cell ends duri ng mitosis, and at the septation site after mitosis. Small amounts of Pom1p are also found at the old cell end during interphase and associa ted with the actin ring during mitosis. Pom1p localization to the cell ends is independent of actin but requires microtubules and Tea1p. pom 1 mutations are synthetically lethal with several other mutations that affect cytokinesis and/or the actin or microtubule cytoskeleton. Thus , Pom1p may position the growth and cytokinesis machineries by interac tion with both the actin and microtubule cytoskeletons.