Wang T, Bretscher A
Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853, USA.
Mol Biol Cell. 1995 Aug;6(8):1011-24. doi: 10.1091/mbc.6.8.1011.
Microfilaments are required for polarized growth and morphogenesis in Saccharomyces cerevisiae. To accomplish this, actin cables and patches are redistributed during the cell cycle to direct secretory components to appropriate sites for cell growth. A major component of actin cables is tropomyosin I, encoded by TPM1, that determines or stabilizes these structures. Disruption of TPM1 is not lethal but results in the loss of actin cables and confers a partial defect in polarized secretion. Using a synthetic lethal screen, we have identified seven mutations residing in six genes whose products are required in the absence of Tpm1p. Each mutant exhibited a morphological defect, suggesting a functional link to the actin cytoskeleton. Complementation cloning of one mutation revealed that it lies in BEM2, which encodes a GTPase-activating protein for the RHO1 product. bem2 mutations also show synthetic lethality with rho1 and mutations in certain other cytoskeletal genes (ACT1, MYO1, MYO2, and SAC6) but not with mutations in several noncytoskeletal genes. These data therefore provide a genetic link between the GAP encoded by BEM2 and the functional organization of microfilaments. In addition, we show that bem2 mutations confer benomyl sensitivity and have abnormal microtubule arrays, suggesting that the BEM2 product may also be involved directly or indirectly in regulating microtubule function.
微丝对于酿酒酵母的极性生长和形态发生是必需的。为实现这一点，肌动蛋白电缆和斑块在细胞周期中重新分布，以将分泌成分引导至细胞生长的合适位点。肌动蛋白电缆的一个主要成分是原肌球蛋白I，由TPM1编码，它决定或稳定这些结构。TPM1的破坏并不致命，但会导致肌动蛋白电缆的丧失，并在极性分泌中造成部分缺陷。通过合成致死筛选，我们鉴定出位于六个基因中的七个突变，其产物在缺乏Tpm1p时是必需的。每个突变体都表现出形态缺陷，表明与肌动蛋白细胞骨架存在功能联系。对一个突变的互补克隆显示它位于BEM2中，BEM2编码RHO1产物的GTP酶激活蛋白。bem2突变也与rho1以及某些其他细胞骨架基因（ACT1、MYO1、MYO2和SAC6）的突变表现出合成致死性，但与几个非细胞骨架基因的突变不表现出合成致死性。因此，这些数据提供了BEM2编码的GAP与微丝功能组织之间的遗传联系。此外，我们表明bem2突变赋予对苯菌灵的敏感性并具有异常的微管阵列，这表明BEM2产物也可能直接或间接参与调节微管功能。
