Amatruda J F, Cannon J F, Tatchell K, Hug C, Cooper J A
Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Nature. 1990 Mar 22;344(6264):352-4. doi: 10.1038/344352a0.
Capping protein controls the addition of actin subunits to the barbed end of actin filaments and nucleates actin polymerization in vitro. Capping protein has been identified in all eukaryotic cells examined so far; it is a heterodimer with subunits of relative molecular masses 32,000-36,000 (alpha-subunit) and 28,000-32,000 (beta-subunit). In skeletal muscle, capping protein (CapZ) probably binds the barbed ends of actin filaments at the Z line. The in vivo role of this protein in non-muscle cells is not known. We report here the characterization of CAP2, the single gene encoding the beta-subunit of capping protein in Saccharomyces cerevisiae. Yeast cells in which the CAP2 gene was disrupted by an insertion or a deletion had an abnormal actin distribution, including the loss of actin cables. The mutant cells were round and large, with a heterogeneous size distribution, and, although viable, grew more slowly than congenic wild-type cells. Chitin, a cell wall component restricted to the mother-bud junction in wild-type budding yeast, was found on the entire mother cell surface in the mutants. The phenotype of CAP2 disruption resembled that of temperature-sensitive mutations in the yeast actin gene ACT1, indicating that capping protein regulates actin-filament distribution in vivo.
封端蛋白可控制肌动蛋白亚基添加到肌动蛋白丝的尖端，并在体外引发肌动蛋白聚合。到目前为止，在所有已检测的真核细胞中均已鉴定出封端蛋白；它是一种异二聚体，由相对分子质量为32,000 - 36,000的亚基（α亚基）和28,000 - 32,000的亚基（β亚基）组成。在骨骼肌中，封端蛋白（CapZ）可能在Z线处结合肌动蛋白丝的尖端。该蛋白在非肌肉细胞中的体内作用尚不清楚。我们在此报告酿酒酵母中编码封端蛋白β亚基的单基因CAP2的特性。CAP2基因通过插入或缺失而被破坏的酵母细胞具有异常的肌动蛋白分布，包括肌动蛋白电缆的丧失。突变细胞呈圆形且较大，大小分布不均，虽然能够存活，但生长速度比同基因野生型细胞慢。几丁质是野生型出芽酵母中仅限于母芽交界处的细胞壁成分，在突变体的整个母细胞表面都有发现。CAP2破坏的表型类似于酵母肌动蛋白基因ACT1中的温度敏感突变，表明封端蛋白在体内调节肌动蛋白丝的分布。
