Imai J, Toh-e A, Matsui Y
Department of Biological Sciences, University of Tokyo, Japan.
Genetics. 1996 Feb;142(2):359-69. doi: 10.1093/genetics/142.2.359.
RHO3 encodes a Rho-type small GTPase of the yeast Saccharomyces cerevisiae. We isolated temperature-sensitive alleles and a dominant active allele of RHO3. Ts- rho3 cells lost cell polarity during bud formation and grew more isotropically than wild-type cells at nonpermissive temperatures. In contrast, cells carrying a dominant active mutant RHO3 displayed cold sensitivity, and the cells became elongated and bent, often at the position where actin patches were concentrated. These phenotypes of the rho3 mutants strongly suggest that RHO3 is involved in directing the growing points during bud formation. In addition, we found that SRO6, previously isolated as a multicopy suppressor of rho3, is the same as SEC4. The sec4-2 mutation was synthetic lethal with temperature-sensitive rho3 mutations and suppressed the cold sensitivity caused by a dominant active mutant RHO3. The genetic interactions between RHO3 and SEC4, taken together with the fact that the Rab-type GTPase Sec4p is required to fuse secretory vesicles together with plasma membrane for exocytosis, support a model in which the Rho3p pathway modulates morphogenesis during bud growth via directing organization of the actin cytoskeleton and the position of the secretory machinery for exocytosis.
RHO3编码酿酒酵母中的一种Rho型小GTP酶。我们分离出了RHO3的温度敏感型等位基因和一个显性活性等位基因。温度敏感型rho3细胞在芽形成过程中失去细胞极性，并且在非允许温度下比野生型细胞更各向同性地生长。相反，携带显性活性突变体RHO3的细胞表现出冷敏感性，并且细胞变得细长且弯曲，通常在肌动蛋白斑集中的位置。rho3突变体的这些表型强烈表明RHO3参与在芽形成过程中引导生长点。此外，我们发现先前作为rho3的多拷贝抑制子分离出的SRO6与SEC4相同。sec4 - 2突变与温度敏感型rho3突变是合成致死的，并抑制了由显性活性突变体RHO3引起的冷敏感性。RHO3和SEC4之间的遗传相互作用，连同Rab型GTP酶Sec4p是将分泌囊泡与质膜融合以进行胞吐作用所必需的这一事实，支持了一个模型，即Rho3p途径通过指导肌动蛋白细胞骨架的组织和胞吐作用的分泌机制的位置来调节芽生长过程中的形态发生。
