Roles of a fimbrin and an alpha-actinin-like protein in fission yeast cell polarization and cytokinesis.
Eukaryotic cells contain many actin-interacting proteins, including the alpha-actinins and the fimbrins, both of which have actin cross-linking activity in vitro. We report here the identification and characterization of both an alpha-actinin-like protein (Ain1p) and a fimbrin (Fim1p) in the fission yeast Schizosaccharomyces pombe. Ain1p localizes to the actomyosin-containing medial ring in an F-actin-dependent manner, and the Ain1p ring contracts during cytokinesis. ain1 deletion cells have no obvious defects under normal growth conditions but display severe cytokinesis defects, associated with defects in medial-ring and septum formation, under certain stress conditions. Overexpression of Ain1p also causes cytokinesis defects, and the ain1 deletion shows synthetic effects with other mutations known to affect medial-ring positioning and/or organization. Fim1p localizes both to the cortical actin patches and to the medial ring in an F-actin-dependent manner, and several lines of evidence suggest that Fim1p is involved in polarization of the actin cytoskeleton. Although a fim1 deletion strain has no detectable defect in cytokinesis, overexpression of Fim1p causes a lethal cytokinesis defect associated with a failure to form the medial ring and concentrate actin patches at the cell middle. Moreover, an ain1 fim1 double mutant has a synthetical-lethal defect in medial-ring assembly and cell division. Thus, Ain1p and Fim1p appear to have an overlapping and essential function in fission yeast cytokinesis. In addition, protein-localization and mutant-phenotype data suggest that Fim1p, but not Ain1p, plays important roles in mating and in spore formation.
Wu
J Q
JQ
Department of Biology and Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill 27599, USA.
Bähler
J
J
Pringle
J R
JR
D000185:Actinin / Q000235:genetics / Q000378:metabolism*; D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002455:Cell Division; D016764:Cell Polarity; D004271:DNA, Fungal; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008840:Microfilament Proteins; D008969:Molecular Sequence Data; D016296:Mutagenesis; D012568:Schizosaccharomyces / Q000166:cytology / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D029702:Schizosaccharomyces pombe Proteins
D000199:Actins; D004271:DNA, Fungal; D005656:Fungal Proteins; D008562:Membrane Glycoproteins; D008840:Microfilament Proteins; D029702:Schizosaccharomyces pombe Proteins; C430383:ain1 protein, S pombe; C026742:plastin; D000185:Actinin