Espinoza F H, Farrell A, Nourse J L, Chamberlin H M, Gileadi O, Morgan D O
Departments of Physiology and Biochemistry & Biophysics, University of California, San Francisco, California 94143-0444, USA.
Mol Cell Biol. 1998 Nov;18(11):6365-73. doi: 10.1128/MCB.18.11.6365.
Complete activation of most cyclin-dependent protein kinases (CDKs) requires phosphorylation by the CDK-activating kinase (CAK). In the budding yeast, Saccharomyces cerevisiae, the major CAK is a 44-kDa protein kinase known as Cak1. Cak1 is required for the phosphorylation and activation of Cdc28, a major CDK involved in cell cycle control. We addressed the possibility that Cak1 is also required for the activation of other yeast CDKs, such as Kin28, Pho85, and Srb10. We generated three new temperature-sensitive cak1 mutant strains, which arrested at the restrictive temperature with nonuniform budding morphology. All three cak1 mutants displayed significant synthetic interactions with loss-of-function mutations in CDC28 and KIN28. Loss of Cak1 function reduced the phosphorylation and activity of both Cdc28 and Kin28 but did not affect the activity of Pho85 or Srb10. In the presence of the Kin28 regulatory subunits Ccl1 and Tfb3, Kin28 was phosphorylated and activated when coexpressed with Cak1 in insect cells. We conclude that Cak1 is required for the activating phosphorylation of Kin28 as well as that of Cdc28.
大多数细胞周期蛋白依赖性蛋白激酶（CDK）的完全激活需要CDK激活激酶（CAK）进行磷酸化。在芽殖酵母酿酒酵母中，主要的CAK是一种44 kDa的蛋白激酶，称为Cak1。Cak1是细胞周期蛋白依赖性激酶28（Cdc28）磷酸化和激活所必需的，Cdc28是参与细胞周期调控的一种主要CDK。我们研究了Cak1是否也是激活其他酵母CDK（如Kin28、Pho85和Srb10）所必需的。我们构建了三个新的温度敏感型cak1突变菌株，它们在限制温度下停滞，芽殖形态不均匀。所有三个cak1突变体与CDC基因28和KIN28功能缺失突变均表现出显著的合成相互作用。Cak1功能的丧失降低了Cdc28和Kin28的磷酸化水平和活性，但不影响Pho85或Srb10的活性。在存在Kin28调节亚基Ccl1和Tfb3的情况下，当Kin28与Cak1在昆虫细胞中共表达时，它会被磷酸化并激活。我们得出结论认为，Cak1是Kin28以及Cdc28激活磷酸化所必需的。
