Centro de Biología Molecular Severo Ochoa (CSIC/UAM), Cantoblanco, 28049 Madrid, Spain.
Nucleic Acids Res. 2012 Sep 1;40(17):8325-35. doi: 10.1093/nar/gks599. Epub 2012 Jun 22.
The conserved heterodimeric endonuclease Mus81-Eme1/Mms4 plays an important role in the maintenance of genomic integrity in eukaryotic cells. Here, we show that budding yeast Mus81-Mms4 is strictly regulated during the mitotic cell cycle by Cdc28 (CDK)- and Cdc5 (Polo-like kinase)-dependent phosphorylation of the non-catalytic subunit Mms4. The phosphorylation of this protein occurs only after bulk DNA synthesis and before chromosome segregation, and is absolutely necessary for the function of the Mus81-Mms4 complex. Consistently, a phosphorylation-defective mms4 mutant shows highly reduced nuclease activity and increases the sensitivity of cells lacking the RecQ-helicase Sgs1 to various agents that cause DNA damage or replicative stress. The mode of regulation of Mus81-Mms4 restricts its activity to a short period of the cell cycle, thus preventing its function during chromosome replication and the negative consequences for genome stability derived from its nucleolytic action. Yet, the controlled Mus81-Mms4 activity provides a safeguard mechanism to resolve DNA intermediates that may remain after replication and require processing before mitosis.
保守的异源二聚体内切核酸酶 Mus81-Eme1/Mms4 在真核细胞基因组完整性的维持中发挥着重要作用。在这里，我们表明，芽殖酵母 Mus81-Mms4 通过 Cdc28（CDK）和 Cdc5（Polo 样激酶）依赖性磷酸化非催化亚基 Mms4 在有丝分裂细胞周期中受到严格调控。该蛋白的磷酸化仅发生在大量 DNA 合成之后和染色体分离之前，对于 Mus81-Mms4 复合物的功能是绝对必要的。一致地，一个磷酸化缺陷的 mms4 突变体显示出高度降低的核酸酶活性，并增加了缺乏 RecQ 解旋酶 Sgs1 的细胞对各种导致 DNA 损伤或复制应激的试剂的敏感性。Mus81-Mms4 的调节方式将其活性限制在细胞周期的一个短暂时期内，从而防止其在染色体复制期间以及其核裂解作用产生的对基因组稳定性的负面影响。然而，受控制的 Mus81-Mms4 活性提供了一种保障机制，以解决复制后可能仍然存在并需要在有丝分裂前进行处理的 DNA 中间产物。
