Howard Hughes Medical Institute, University of California, Davis, Davis, California, USA; Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA.
Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, USA.
Mol Cell. 2020 Apr 2;78(1):168-183.e5. doi: 10.1016/j.molcel.2020.02.001. Epub 2020 Mar 3.
Crossover recombination is essential for accurate chromosome segregation during meiosis. The MutSγ complex, Msh4-Msh5, facilitates crossing over by binding and stabilizing nascent recombination intermediates. We show that these activities are governed by regulated proteolysis. MutSγ is initially inactive for crossing over due to an N-terminal degron on Msh4 that renders it unstable by directly targeting proteasomal degradation. Activation of MutSγ requires the Dbf4-dependent kinase Cdc7 (DDK), which directly phosphorylates and thereby neutralizes the Msh4 degron. Genetic requirements for Msh4 phosphorylation indicate that DDK targets MutSγ only after it has bound to nascent joint molecules (JMs) in the context of synapsing chromosomes. Overexpression studies confirm that the steady-state level of Msh4, not phosphorylation per se, is the critical determinant for crossing over. At the DNA level, Msh4 phosphorylation enables the formation and crossover-biased resolution of double-Holliday Junction intermediates. Our study establishes regulated protein degradation as a fundamental mechanism underlying meiotic crossing over.
交叉重组对于减数分裂过程中染色体的正确分离至关重要。MutSγ 复合物（Msh4-Msh5）通过结合和稳定新生重组中间体来促进交叉重组。我们表明，这些活性受调节蛋白水解控制。MutSγ 最初对于交叉重组是无活性的，因为 Msh4 上存在 N 端降解结构域，该结构域通过直接靶向蛋白酶体降解使 Msh4 不稳定。MutSγ 的激活需要 Dbf4 依赖性激酶 Cdc7（DDK），后者直接磷酸化并因此中和 Msh4 降解结构域。Msh4 磷酸化的遗传要求表明，DDK 仅在 MutSγ 结合到联会染色体背景中的新生连接分子（JMs）后才靶向 MutSγ。过表达研究证实，Msh4 的稳态水平，而不是磷酸化本身，是交叉重组的关键决定因素。在 DNA 水平上，Msh4 磷酸化可促进双 Holliday 连接中间体的形成和交叉重组偏向性解析。我们的研究确立了调节蛋白降解作为减数分裂交叉重组的基本机制。
