title: Septin ring assembly requires concerted action of polarisome components, a PAK kinase Cla4p, and the actin cytoskeleton in Saccharomyces cerevisiae.
abstract: Septins are filament-forming proteins that function in cytokinesis in a wide variety of organisms. In budding yeast, the small GTPase Cdc42p triggers the recruitment of septins to the incipient budding site and the assembly of septins into a ring. We herein report that Bni1p and Cla4p, effectors of Cdc42p, are required for the assembly of the septin ring during the initiation of budding but not for its maintenance after the ring converts to a septin collar. In bni1Delta cla4-75-td mutant, septins were recruited to the incipient budding site. However, the septin ring was not assembled, and septins remained at the polarized growing sites. Bni1p, a formin family protein, is a member of the polarisome complex with Spa2p, Bud6p, and Pea2p. All spa2Delta cla4-75-td, bud6Delta cla4-75-td, and pea2Delta cla4-75-td mutants showed defects in septin ring assembly. Bni1p stimulates actin polymerization for the formation of actin cables. Point mutants of BNI1 that are specifically defective in actin cable formation also exhibited septin ring assembly defects in the absence of Cla4p. Consistently, treatment of cla4Delta mutant with the actin inhibitor latrunculin A inhibited septin ring assembly. Our results suggest that polarisome components and Cla4p are required for the initial assembly of the septin ring and that the actin cytoskeleton is involved in this process.
authors.affiliation: Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Medicine, N15 W7, Kita-ku, Sapporo, 060-0815, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Kadota
authors.forename: Takaharu
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Shiro
authors.initials: S
authors.lastname: Yoshiuchi
authors.forename: Erfei
authors.initials: E
authors.lastname: Bi
authors.forename: Kazuma
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D000199:Actins / Q000378:metabolism*; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D016764:Cell Polarity; D049109:Cell Proliferation; D003599:Cytoskeleton / Q000235:genetics / Q000378:metabolism*; D008840:Microfilament Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; C105191:Bni1 protein, S cerevisiae; D018797:Cell Cycle Proteins; D008840:Microfilament Proteins; D029701:Saccharomyces cerevisiae Proteins; C095212:CLA4 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D020764:cdc42 GTP-Binding Protein