GENETIC-ANALYSIS OF CELL MORPHOGENESIS IN FISSION YEAST - A ROLE FOR CASEIN KINASE-II IN THE ESTABLISHMENT OF POLARIZED GROWTH

We hare initiated a study to identify genes regulating cell morphogene sis in the fission yeast Schizosaccharomyces pombe. Five genes have be en identified, orb1-orb5, whose mutation gives rise to spherical cells , indicative of an inability to polarize growth. Two further genes hav e been identified, teal and ban1, whose mutant alleles have disturbed patterns of tip growth, leading to T-shaped and curved cells. In fissi on yeast, sites of cell wall deposition are defined by actin localizat ion, with actin distributions and therefore growth patterns undergoing cell cycle stage-specific reorganization. Studies of double mutants c onstructed between orb5-19 and various cdc mutants blocked before and after cell division show that orb5 is required for the re-establishmen t of polar growth following cytokinesis. This indicates that the mutan t allele orb5-19 is defective in the reinitiation of polarized growth, even though actin reorganization to the cell tips occurs normally. or b5 encodes a fission yeast homologue of casein kinase II alpha. We pro pose that this kinase plays a role in the translation of cell polarity into polarized growth, but not in the establishment of polarity itsel f.