Marquitz Aron R, Harrison Jacob C, Bose Indrani, Zyla Trevin R, McMillan John N, Lew Daniel J
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA.
EMBO J. 2002 Aug 1;21(15):4012-25. doi: 10.1093/emboj/cdf416.
The Saccharomyces cerevisiae morphogenesis checkpoint delays mitosis in response to insults that impair actin organization and/or bud formation. The delay is due to accumulation of the inhibitory kinase Swe1p, which phosphorylates the cyclin-dependent kinase Cdc28p. Having screened through a panel of yeast mutants with defects in cell morphogenesis, we report here that the polarity establishment protein Bem2p is required for the checkpoint response. Bem2p is a Rho-GTPase activating protein (GAP) previously shown to act on Rho1p, and we now show that it also acts on Cdc42p, the GTPase primarily responsible for establishment of cell polarity in yeast. Whereas the morphogenesis role of Bem2p required GAP activity, the checkpoint role of Bem2p did not. Instead, this function required an N-terminal Bem2p domain. Thus, this single protein has a GAP-dependent role in promoting cell polarity and a GAP-independent role in responding to defects in cell polarity by enacting the checkpoint. Surprisingly, Swe1p accumulation occurred normally in bem2 cells, but they were nevertheless unable to promote Cdc28p phosphorylation. Therefore, Bem2p defines a novel pathway in the morphogenesis checkpoint.
酿酒酵母形态发生检查点会因损害肌动蛋白组织和/或芽形成的损伤而延迟有丝分裂。这种延迟是由于抑制性激酶Swe1p的积累，它会使细胞周期蛋白依赖性激酶Cdc28p磷酸化。在筛选了一组细胞形态发生存在缺陷的酵母突变体后，我们在此报告极性建立蛋白Bem2p是检查点反应所必需的。Bem2p是一种Rho - GTPase激活蛋白（GAP），先前已证明它作用于Rho1p，我们现在表明它也作用于Cdc42p，Cdc42p是酵母中主要负责建立细胞极性的GTPase。虽然Bem2p的形态发生作用需要GAP活性，但Bem2p的检查点作用则不需要。相反，该功能需要Bem2p的N端结构域。因此，这种单一蛋白质在促进细胞极性方面具有依赖GAP的作用，而在通过启动检查点来应对细胞极性缺陷方面具有不依赖GAP的作用。令人惊讶的是，Swe1p在bem2细胞中正常积累，但它们仍然无法促进Cdc28p磷酸化。因此，Bem2p在形态发生检查点中定义了一条新途径。
