Calzada A, Sacristán M, Sánchez E, Bueno A
Instituto de Microbiología-Bioquímica, Departemento de Microbiología y Genética, Universidad de Salamanca, CSIC, Spain.
Nature. 2001 Jul 19;412(6844):355-8. doi: 10.1038/35085610.
Exit from mitosis requires the inactivation of mitotic cyclin-dependent kinases (CDKs). In the budding yeast, Saccharomyces cerevisiae, inactivation of CDKs during late mitosis involves degradation of B-type cyclins as well as direct inhibition of cyclin-CDK complexes by the CDK-inhibitor protein Sic1 (refs 1,2,3). Several striking similarities exist between Sic1 and Cdc6, a DNA replication factor essential for the formation of pre-replicative complexes at origins of DNA replication. Transcription of both genes is activated during late mitosis by a process dependent on Swi5 (ref. 10). Like Sic1, Cdc6 binds CDK complexes in vivo and downregulates them in vitro. Here we show that Cdc6, like Sic1, also contributes to inactivation of CDKs during late mitosis in S. cerevisiae. Deletion of the CDK-interacting domain of Cdc6 does not inhibit the function of origins of DNA replication during S phase, but instead causes a delay in mitotic exit; this delay is accentuated in the absence of Sic1 or of cyclin degradation. By contributing to mitotic exit and inactivation of CDKs, Cdc6 helps to create the conditions that are required for its subsequent role in the formation of pre-replicative complexes at origins of DNA replication.
从有丝分裂中退出需要有丝分裂周期蛋白依赖性激酶（CDK）失活。在芽殖酵母酿酒酵母中，有丝分裂后期CDK的失活涉及B型细胞周期蛋白的降解以及CDK抑制蛋白Sic1对细胞周期蛋白-CDK复合物的直接抑制（参考文献1、2、3）。Sic1与Cdc6之间存在一些显著的相似之处，Cdc6是一种DNA复制因子，对于在DNA复制起点形成前复制复合物至关重要。这两个基因的转录在有丝分裂后期通过一个依赖于Swi5的过程被激活（参考文献10）。与Sic1一样，Cdc6在体内结合CDK复合物并在体外下调它们的活性。我们在此表明，与Sic1一样，Cdc6在酿酒酵母有丝分裂后期也有助于CDK的失活。缺失Cdc6的CDK相互作用结构域不会抑制S期DNA复制起点的功能，反而会导致有丝分裂退出延迟；在没有Sic1或细胞周期蛋白降解的情况下，这种延迟会更加明显。通过促进有丝分裂退出和CDK失活，Cdc6有助于创造其随后在DNA复制起点形成前复制复合物过程中发挥作用所需的条件。
