Isolation and analysis of new genes that regulate the actin cytoskeleton system

肌动蛋白细胞骨架系统在细胞运动、细胞间黏附、细胞极性形成、细胞形态变化等方面发挥着重要作用。I型肌球蛋白是一种不依赖肌动蛋白的运动蛋白，参与肌动蛋白细胞骨架的重组和内吞作用。Myo3p和Myo5p是发芽酵母中的I型肌球蛋白。在这项研究中，我们分离了一个新的基因CDC50，作为myo5突变体的多拷贝抑制基因。Cdc50突变体最初被鉴定为细胞分裂周期停滞的突变体，但其功能尚未确定。CDC50编码一个具有跨膜结构域的膜蛋白。生化实验表明，CDC50P是一种完整的膜蛋白。对表达CDC50-GFP的细胞的显微镜观察表明，CDC50定位于内体，提示CDC50参与了通过内体的蛋白质或脂类运输。Cdc50突变体表现出冷敏感的生长表型，细胞停滞在小芽期，这表明cdc50p调节细胞极化。对cdc50突变体中肌动蛋白细胞骨架的可视化显示，在cdc50突变体中肌动蛋白斑块被非局部化。我们的结果表明，CDC50调节一种与肌动蛋白细胞骨架极化有关的蛋白质到质膜的运输。

The actin cytoskeleton system plays an important role in cell motility, cell-cell adhesion, formation of cell polarity, and cell morphological change. Type I myosins are actindependent motor proteins and are involved in the reorganization of the actin cytoskeleton and endocytosis. Myo3p and Myo5p are the type I myosins in the budding yeast Saccharomyces cerevisiae. In this study, we have isolated a new gene, CDC50, as a multicopy suppressor of the myo5 mutant. The cdc50 mutant was first characterized as a mutant which show cell division cycle arrest, but its functions has not been characterized yet. CDC50 encodes a putative membrane protein that possesses a transmembrane domain. Biochemical experiments indicate that Cdc50p is an integral membrane protein. Microscopic observation of cells expressing CDC50-GFP indicates that CDC50 is localized to endosomes, suggesting that CDC50 is involved in the protein or lipid traffic through endosomes. The cdc50 mutant shows a coldsensitive growth phenotype and cells are arrested at small-budded stage, suggesting that Cdc50p regulates cell polarization. Visualization of the actin cytoskeleton in the cdc50 mutant revealed that actin patches are delocalized in the cdc50 mutant. Our results indicate that CDC50 regulates a traffic to the plasma membrane of a protein that is involved in the polarization of the actin cytoskeleton.