Dynamic localization and function of Bni1p at the sites of directed growth in Saccharomyces cerevisiae.
Formin homology (FH) proteins are implicated in cell polarization and cytokinesis through actin organization. There are two FH proteins in the yeast Saccharomyces cerevisiae, Bni1p and Bnr1p. Bni1p physically interacts with Rho family small G proteins (Rho1p and Cdc42p), actin, two actin-binding proteins (profilin and Bud6p), and a polarity protein (Spa2p). Here we analyzed the in vivo localization of Bni1p by using a time-lapse imaging system and investigated the regulatory mechanisms of Bni1p localization and function in relation to these interacting proteins. Bni1p fused with green fluorescent protein localized to the sites of cell growth throughout the cell cycle. In a small-budded cell, Bni1p moved along the bud cortex. This dynamic localization of Bni1p coincided with the apparent site of bud growth. A bni1-disrupted cell showed a defect in directed growth to the pre-bud site and to the bud tip (apical growth), causing its abnormally spherical cell shape and thick bud neck. Bni1p localization at the bud tips was absolutely dependent on Cdc42p, largely dependent on Spa2p and actin filaments, and partly dependent on Bud6p, but scarcely dependent on polarized cortical actin patches or Rho1p. These results indicate that Bni1p regulates polarized growth within the bud through its unique and dynamic pattern of localization, dependent on multiple factors, including Cdc42p, Spa2p, Bud6p, and the actin cytoskeleton.
Ozaki-Kuroda
K
K
Department of Molecular Biology and Biochemistry, Osaka University Graduate School of Medicine/Faculty of Medicine, Suita, Osaka 565-0871, Japan.
Yamamoto
Y
Y
Nohara
H
H
Kinoshita
M
M
Fujiwara
T
T
Irie
K
K
Takai
Y
Y
D000199:Actins / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D001693:Biological Transport, Active; D016764:Cell Polarity; D003598:Cytoskeletal Proteins; D017931:DNA Primers / Q000235:genetics; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism
D000199:Actins; C107727:BUD6 protein, S cerevisiae; C105191:Bni1 protein, S cerevisiae; D003598:Cytoskeletal Proteins; D017931:DNA Primers; D005656:Fungal Proteins; D008164:Luminescent Proteins; D008840:Microfilament Proteins; D011993:Recombinant Fusion Proteins; C065889:SPA2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D049452:Green Fluorescent Proteins; C051302:RHO1 protein, S cerevisiae; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; D020741:rho GTP-Binding Proteins