Wu J Q, Bähler J, Pringle J R
Department of Biology and Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill 27599, USA.
Mol Biol Cell. 2001 Apr;12(4):1061-77. doi: 10.1091/mbc.12.4.1061.
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.
真核细胞含有许多与肌动蛋白相互作用的蛋白质，包括α - 辅肌动蛋白和丝束蛋白，这两种蛋白在体外均具有肌动蛋白交联活性。我们在此报告在裂殖酵母粟酒裂殖酵母中鉴定并表征了一种α - 辅肌动蛋白样蛋白（Ain1p）和一种丝束蛋白（Fim1p）。Ain1p以F - 肌动蛋白依赖的方式定位于含肌动球蛋白的中间环，并且在胞质分裂期间Ain1p环会收缩。缺失ain1的细胞在正常生长条件下没有明显缺陷，但在某些应激条件下会表现出严重的胞质分裂缺陷，这与中间环和隔膜形成的缺陷有关。Ain1p的过表达也会导致胞质分裂缺陷，并且缺失ain1与其他已知影响中间环定位和/或组织的突变显示出合成效应。Fim1p以F - 肌动蛋白依赖的方式定位于皮质肌动蛋白斑和中间环，并且有几条证据表明Fim1p参与肌动蛋白细胞骨架的极化。尽管缺失fim1的菌株在胞质分裂中没有可检测到的缺陷，但Fim1p的过表达会导致致命的胞质分裂缺陷，这与无法形成中间环以及肌动蛋白斑在细胞中部集中有关。此外，ain1 fim1双突变体在中间环组装和细胞分裂方面具有合成致死缺陷。因此，Ain1p和Fim1p在裂殖酵母胞质分裂中似乎具有重叠且必不可少的功能。此外，蛋白质定位和突变体表型数据表明，Fim1p而非Ain1p在交配和孢子形成中起重要作用。
