Altman R, Kellogg D
Sinsheimer Laboratories, Department of Biology, University of California, Santa Cruz, California 95064, USA.
J Cell Biol. 1997 Jul 14;138(1):119-30. doi: 10.1083/jcb.138.1.119.
Little is known about the pathways used by cyclins and cyclin-dependent kinases to induce the events of the cell cycle. In budding yeast, a protein called Nap1 binds to the mitotic cyclin Clb2, and Nap1 is required for the ability of Clb2 to induce specific mitotic events, but the role played by Nap1 is unclear. We have used genetic and biochemical approaches to identify additional proteins that function with Nap1 in the control of mitotic events. These approaches have both identified a protein kinase called Gin4 that is required for the ability of Clb2 and Nap1 to promote the switch from polar to isotropic bud growth that normally occurs during mitosis. Gin4 is also required for the ability of Clb2 and Nap1 to promote normal progression through mitosis. The Gin4 protein becomes phosphorylated as cells enter mitosis, resulting in the activation of Gin4 kinase activity, and the phosphorylation of Gin4 is dependent upon Nap1 and Clb2 in vivo. Affinity chromatography experiments demonstrate that Gin4 binds tightly to Nap1, indicating that the functions of these two proteins are closely tied within the cell. These results demonstrate that the activation of Gin4 is under the control of Clb2 and Nap1, and they provide an important step towards elucidating the molecular pathways that link cyclin-dependent kinases to the events they control.
关于细胞周期蛋白和细胞周期蛋白依赖性激酶用于诱导细胞周期事件的途径，人们了解得很少。在芽殖酵母中，一种名为Nap1的蛋白质与有丝分裂细胞周期蛋白Clb2结合，并且Nap1是Clb2诱导特定有丝分裂事件能力所必需的，但Nap1所起的作用尚不清楚。我们已经使用遗传和生化方法来鉴定在有丝分裂事件控制中与Nap1一起发挥作用的其他蛋白质。这些方法都鉴定出一种名为Gin4的蛋白激酶，它是Clb2和Nap1促进从极性芽生长向通常在有丝分裂期间发生的各向同性芽生长转变的能力所必需的。Gin4也是Clb2和Nap1促进有丝分裂正常进行的能力所必需的。随着细胞进入有丝分裂，Gin4蛋白会被磷酸化，从而导致Gin4激酶活性的激活，并且在体内Gin4的磷酸化依赖于Nap1和Clb2。亲和层析实验表明Gin4与Nap1紧密结合，这表明这两种蛋白质的功能在细胞内紧密相关。这些结果表明Gin4的激活受Clb2和Nap1的控制，并且它们为阐明将细胞周期蛋白依赖性激酶与其所控制的事件联系起来的分子途径迈出了重要的一步。
