Mack D, Nishimura K, Dennehey B K, Arbogast T, Parkinson J, Toh-e A, Pringle J R, Bender A, Matsui Y
Department of Biology, Indiana University, Bloomington 47405, USA.
Mol Cell Biol. 1996 Aug;16(8):4387-95. doi: 10.1128/MCB.16.8.4387.
The Rho-type GTPase Cdc42p is required for cell polarization and bud emergence in Saccharomyces cerevisiae. To identify genes whose functions are linked to CDC42, we screened for (i) multicopy suppressors of a Ts- cdc42 mutant, (ii) mutants that require multiple copies of CDC42 for survival, and (iii) mutations that display synthetic lethality with a partial-loss-of-function allele of CDC24, which encodes a guanine nucleotide exchange factor for Cdc42p. In all three screens, we identified a new gene, BEM4. Cells from which BEM4 was deleted were inviable at 37 degrees C. These cells became unbudded, large, and round, consistent with a model in which Bem4p acts together with Cdc42p in polarity establishment and bud emergence. In some strains, the ability of CDC42 to serve as a multicopy suppressor of the Ts- growth defect of deltabem4 cells required co-overexpression of Rho1p, which is an essential Rho-type GTPase necessary for cell wall integrity. This finding suggests that Bem4p also affects Rho1p function. Bem4p displayed two-hybrid interactions with Cdc42p, Rho1p, and two of the three other known yeast Rho-type GTPases, suggesting that Bem4p can interact with multiple Rho-type GTPases. Models for the role of Bem4p include that it serves as a chaperone or modulates the interaction of these GTPases with one or more of their targets or regulators.
Rho 型 GTP 酶 Cdc42p 是酿酒酵母细胞极化和芽出现所必需的。为了鉴定其功能与 CDC42 相关的基因，我们进行了以下筛选：（i）温度敏感型 cdc42 突变体的多拷贝抑制子；（ii）需要多个 CDC42 拷贝才能存活的突变体；（iii）与 CDC24 的部分功能丧失等位基因表现出合成致死性的突变，CDC24 编码 Cdc42p 的鸟嘌呤核苷酸交换因子。在所有这三项筛选中，我们鉴定出一个新基因 BEM4。缺失 BEM4 的细胞在 37℃时无法存活。这些细胞变得无芽、变大且呈圆形，这与 Bem4p 在极性建立和芽出现过程中与 Cdc42p 共同发挥作用的模型一致。在一些菌株中，CDC42 作为 deltabem4 细胞 Ts 生长缺陷的多拷贝抑制子的能力需要 Rho1p 的共过表达，Rho1p 是细胞壁完整性所必需的一种重要的 Rho 型 GTP 酶。这一发现表明 Bem4p 也影响 Rho1p 的功能。Bem4p 与 Cdc42p、Rho1p 以及其他三种已知酵母 Rho 型 GTP 酶中的两种显示出双杂交相互作用，表明 Bem4p 可以与多种 Rho 型 GTP 酶相互作用。Bem4p 的作用模型包括它作为一种伴侣蛋白或调节这些 GTP 酶与其一个或多个靶标或调节因子之间的相互作用。
