Katayama S, Hirata D, Arellano M, Pérez P, Toda T
Laboratory of Cell Regulation, Imperial Cancer Research Fund, London WC2A 3PX, United Kingdom.
J Cell Biol. 1999 Mar 22;144(6):1173-86. doi: 10.1083/jcb.144.6.1173.
In fission yeast protein kinase C homologues (Pck1 and Pck2) are essential for cell morphogenesis. We have isolated mok1(+) in a genetic screen to identify downstream effectors for Pck1/2. mok1(+) is essential for viability and encodes a protein that has several membrane-spanning domains and regions homologous to glucan metabolic enzymes. mok1 mutant shows abnormal cell shape, randomization of F-actin and weak cell wall. Biochemical analysis shows that Mok1 appears to have alpha-glucan synthase activity. Mok1 localization undergoes dramatic alteration during the cell cycle. It localizes to the growing tips in interphase, the medial ring upon mitosis, a double ring before and dense dot during cytokinesis. Double immunofluorescence staining shows that Mok1 exists in close proximity to actin. The subcellular localization of Mok1 is dependent upon the integrity of the F-actin cytoskeleton. Conversely, overexpression of mok1(+) blocks the translocation of cortical actin from one end of the cell to the other. pck2 mutant is synthetically lethal with mok1 mutant, delocalizes Mok1 and shows a lower level of alpha-glucan. These results indicate that Mok1 plays a crucial role in cell morphogenesis interdependently of the actin cytoskeleton and works as one of downstream effectors for Pck1/2.
在裂殖酵母中，蛋白激酶C同源物（Pck1和Pck2）对细胞形态发生至关重要。我们在一项基因筛选中分离出了mok1(+)，以鉴定Pck1/2的下游效应物。mok1(+)对细胞存活至关重要，编码一种具有多个跨膜结构域以及与葡聚糖代谢酶同源区域的蛋白质。mok1突变体表现出异常的细胞形态、F-肌动蛋白分布紊乱以及细胞壁薄弱。生化分析表明，Mok1似乎具有α-葡聚糖合酶活性。Mok1的定位在细胞周期中发生显著变化。在间期它定位于生长尖端，有丝分裂时定位于中间环，胞质分裂前为双环，胞质分裂期间为致密点。双重免疫荧光染色显示，Mok1与肌动蛋白紧密相邻。Mok1的亚细胞定位取决于F-肌动蛋白细胞骨架的完整性。相反，mok1(+)的过表达会阻止皮质肌动蛋白从细胞一端向另一端的转运。pck2突变体与mok1突变体发生合成致死，使Mok1定位异常，并显示出较低水平的α-葡聚糖。这些结果表明，Mok1在细胞形态发生中依赖于肌动蛋白细胞骨架发挥关键作用，并作为Pck1/2的下游效应物之一发挥作用。
