Roles of a fimbrin and an alpha-actinin-like protein in fission yeast cell polarization and cytokinesis.

Department of Biology and Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill 27599, USA.
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.
Mesh Terms:
Actinin, Actins, Amino Acid Sequence, Animals, Base Sequence, Cell Division, Cell Polarity, DNA, Fungal, Fungal Proteins, Membrane Glycoproteins, Microfilament Proteins, Molecular Sequence Data, Mutagenesis, Schizosaccharomyces, Schizosaccharomyces pombe Proteins
Mol. Biol. Cell Apr. 01, 2001; 12(4);1061-77 [PUBMED:11294907]
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