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首页> 外文期刊>Molecular and Cellular Biology >Distinct Phosphoisoforms of the XenopusMcm4 Protein Regulate the Function of the Mcm Complex
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Distinct Phosphoisoforms of the XenopusMcm4 Protein Regulate the Function of the Mcm Complex

机译：XenopusMcm4蛋白的不同磷亚型调节Mcm复合物的功能。

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Initiation of DNA replication in eukaryotes requires the assembly of prereplication complexes (pre-Rcs) at the origins of replication. The assembly and function of the pre-Rcs appear to be controlled by phosphorylation events. In this study we report the detailed characterization of the cell cycle phosphorylation of one component of the Xenopus pre-Rcs, the Mcm protein complex. We show that individual Mcm subunits are differentially phosphorylated during the cell cycle. During mitosis, the Mcm4 subunit is hyperphosphorylated, while the other subunits are not actively phosphorylated. The mitotic phosphorylation of Mcm4 requires Cdc2-cyclin B and other unknown kinases. Following exit from mitosis, the Mcm4 subunit of the cytosolic interphase complex undergoes dephosphorylation, and the Mcm2, Mcm3, or Mcm6 subunits are then actively phosphorylated by kinase(s) other than cyclin-dependent kinases (Cdks) or Cdc7. The association of the Mcm complex with the pre-Rcs correlates with the formation of a transient interphase complex. This complex contains an intermediately phosphorylated Mcm4 subunit and is produced by partial dephosphorylation of the mitotic hyperphosphorylated Mcm4 protein. Complete dephosphorylation of the Mcm4 subunit inactivates the Mcm complex and prevents its binding to the chromatin. Once the Mcm complex is assembled on the chromatin the Mcm4 and the Mcm2 proteins are the only subunits phosphorylated during the activation of the pre-Rcs. These chromatin-associated phosphorylations require nuclear transport and are independent of Cdk2-cyclin E. These results suggest that the changes in Mcm4 phosphorylation regulate pre-Rc assembly and the function of the pre-Rcs on the chromatin.
机译：在真核生物中DNA复制的启动需要在复制起点处组装复制前复合物（pre-Rcs）。 pre-Rcs的组装和功能似乎受磷酸化事件控制。在这项研究中，我们报告了非洲爪蟾（Xem） pre-Rcs（Mcm蛋白复合物）一种成分的细胞周期磷酸化的详细表征。我们显示单个Mcm亚基在细胞周期中差异磷酸化。在有丝分裂期间，Mcm4亚基被过度磷酸化，而其他亚基没有被主动磷酸化。 Mcm4的有丝分裂磷酸化需要Cdc2-cyclin B和其他未知的激酶。从有丝分裂退出后，胞质间期复合物的Mcm4亚基进行去磷酸化，然后Mcm2，Mcm3或Mcm6亚基被细胞周期蛋白依赖性激酶（Cdks）或Cdc7以外的激酶主动磷酸化。 Mcm复合物与pre-Rcs的关联与瞬态相间复合物的形成相关。该复合物包含一个中间磷酸化的Mcm4亚基，是通过有丝分裂的超磷酸化Mcm4蛋白的部分去磷酸化产生的。 Mcm4亚基的完全去磷酸化使Mcm复合物失活并阻止其与染色质结合。一旦将Mcm复合物装配在染色质上，则Mcm4和Mcm2蛋白是pre-Rcs激活过程中唯一被磷酸化的亚基。这些与染色质相关的磷酸化需要核转运，并且独立于Cdk2-cyclinE。这些结果表明，Mcm4磷酸化的改变调节了Pre-Rc装配和染色质上Rc-pre的功能。

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