Lin Douglas I, Aggarwal Priya, Diehl J Alan
The Leonard and Madlyn Abramson Family Cancer Research Institute and Cancer Center, University of Pennsylvania, Philadelphia, PA 19104, USA.
Proc Natl Acad Sci U S A. 2008 Jun 10;105(23):8079-84. doi: 10.1073/pnas.0800077105. Epub 2008 Jun 4.
During late M and early G(1), MCM2-7 assembles and is loaded onto chromatin in the final step of prereplicative complex (pre-RC) formation. However, the regulation of MCM assembly remains poorly understood. Cyclin-dependent kinase (CDK)-dependent phosphorylation contributes to DNA replication by initially activating pre-RCs and subsequently inhibiting refiring of origins during S and M phases, thus limiting DNA replication to a single round. Although the precise roles of specific MCM phosphorylation events are poorly characterized, we now demonstrate that CDK1 phosphorylates MCM3 at Ser-112, Ser-611, and Thr-719. In vivo, CDK1-dependent phosphorylation of Ser-112 triggers the assembly of MCM3 with the remaining MCM subunits and subsequent chromatin loading of MCMs. Strikingly, loss of MCM3 triggers the destabilization of other MCM proteins, suggesting that phosphorylation-dependent assembly is essential for stable accumulation of MCM proteins. These data reveal that CDK-dependent MCM3 phosphorylation contributes to the regulated formation of the MCM2-7 complex.
在有丝分裂晚期（M期）和G1期早期，MCM2 - 7组装并在复制前复合体（pre - RC）形成的最后一步加载到染色质上。然而，MCM组装的调控仍知之甚少。细胞周期蛋白依赖性激酶（CDK）依赖性磷酸化通过最初激活pre - RC以及随后在S期和M期抑制起始点的重新激发来促进DNA复制，从而将DNA复制限制为单轮。尽管特定MCM磷酸化事件的确切作用尚未得到充分表征，但我们现在证明CDK1在Ser - 112、Ser - 611和Thr - 719位点磷酸化MCM3。在体内，Ser - 112的CDK1依赖性磷酸化触发MCM3与其余MCM亚基的组装以及随后MCMs的染色质加载。引人注目的是，MCM3的缺失会引发其他MCM蛋白的不稳定，这表明磷酸化依赖性组装对于MCM蛋白的稳定积累至关重要。这些数据表明，CDK依赖性的MCM3磷酸化有助于MCM2 - 7复合体的调控形成。
