title: Pom1 DYRK regulates localization of the Rga4 GAP to ensure bipolar activation of Cdc42 in fission yeast.
abstract: BACKGROUND
  In the fission yeast Schizosaccharomyces pombe, cell growth takes place exclusively at both ends of the cylindrical cell. During this highly polarized growth, microtubules are responsible for the placement of the cell-end marker proteins, the Tea1-Tea4/Wsh3 complex, which recruits the Pom1 DYRK-family protein kinase. Pom1 is required for proper positioning of growth sites, and the Deltapom1 mutation brings about monopolar cell growth.
  
  
  RESULTS
  Pom1 kinase physically interacts with Rga4, which has a GAP (GTPase-activating protein) domain for Rho-family GTPase. Genetic and biochemical evidence indicates that Rga4 functions as GAP for the Cdc42 GTPase, an evolutionarily conserved regulator of F-actin. CRIB (Cdc42/Rac interactive binding)-GFP microscopy has revealed that GTP-bound, active Cdc42 is concentrated to growing cell ends accompanied by developed F-actin structures, where the Rga4 GAP is excluded. The monopolar Deltapom1 mutant fails to eliminate Rga4 from the nongrowing cell end, resulting in monopolar distribution of GTP-Cdc42 to the growing cell end. However, mutational inactivation of Rga4 allows Cdc42 to be active at both ends of Deltapom1 cells, suggesting that mislocalization of Rga4 in the Deltapom1 mutant contributes to its monopolar phenotype.
  
  
  CONCLUSIONS
  Pom1 kinase recruited to cell ends by the Tea1-Tea4/Wsh3 complex is essential for proper localization of a GAP for Cdc42, Rga4, which ensures bipolar localization of GTP-bound, active Cdc42. Because of the established role of Cdc42 in F-actin formation, these observations provide a new insight into how the microtubule system achieves localized formation of F-actin to generate cell polarity.
authors.affiliation: Section of Microbiology, College of Biological Sciences, University of California, Davis, California 95616, USA.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Tatebe
authors.forename: Kentaro
authors.initials: K
authors.lastname: Nakano
authors.forename: Rachel
authors.initials: R
authors.lastname: Maximo
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Shiozaki
mesh_terms: D000199:Actins / Q000378:metabolism; D049108:Cell Enlargement; D016764:Cell Polarity / Q000502:physiology*; D003599:Cytoskeleton / Q000502:physiology*; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012568:Schizosaccharomyces / Q000201:enzymology*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*; D000097603:Dyrk Kinases
chemical_list: D000199:Actins; D020690:GTPase-Activating Proteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D029702:Schizosaccharomyces pombe Proteins; D020764:cdc42 GTP-Binding Protein; D000097603:Dyrk Kinases; C529495:Rga4 protein, S pombe; C112212:Pom1 protein, S pombe