Institute of Biochemistry, ETH Zürich, Otto-Stern-Weg 3, 8093 Zürich, Switzerland.
Institute for Research in Biomedicine, Faculty of Biomedical Sciences, Università della Svizzera Italiana (USI), Bellinzona, 6500, Switzerland.
Dev Cell. 2020 Jun 22;53(6):706-723.e5. doi: 10.1016/j.devcel.2020.05.016. Epub 2020 Jun 5.
The Bloom's helicase ortholog, Sgs1, orchestrates the formation and disengagement of recombination intermediates to enable controlled crossing-over during meiotic and mitotic DNA repair. Whether its enzymatic activity is temporally regulated to implement formation of noncrossovers prior to the activation of crossover-nucleases is unknown. Here, we show that, akin to the Mus81-Mms4, Yen1, and MutLγ-Exo1 nucleases, Sgs1 helicase function is under cell-cycle control through the actions of CDK and Cdc5 kinases. Notably, however, whereas CDK and Cdc5 unleash nuclease function during M phase, they act in concert to stimulate Sgs1 activity during S phase/prophase I. Mechanistically, CDK-mediated phosphorylation enhances the velocity and processivity of Sgs1, which stimulates DNA unwinding in vitro and joint molecule processing in vivo. Subsequent hyper-phosphorylation by Cdc5 appears to reduce the activity of Sgs1, while activating Mus81-Mms4 and MutLγ-Exo1. These findings suggest a concerted mechanism driving orderly formation of noncrossover and crossover recombinants in meiotic and mitotic cells.
布卢姆解旋酶同源物 Sgs1 协调重组中间体的形成和脱离，以实现减数分裂和有丝分裂 DNA 修复过程中的受控交叉。其酶活性是否通过时间调节来实现非交叉的形成，然后再激活交叉核酸酶，目前尚不清楚。在这里，我们表明，类似于 Mus81-Mms4、Yen1 和 MutLγ-Exo1 核酸酶，Sgs1 解旋酶的功能受细胞周期控制，通过 CDK 和 Cdc5 激酶的作用。值得注意的是，然而，尽管 CDK 和 Cdc5 在 M 期释放核酸酶功能，但它们在 S 期/前期 I 中协同作用以刺激 Sgs1 活性。从机制上讲，CDK 介导的磷酸化增强了 Sgs1 的速度和持续性，从而刺激了体外 DNA 解旋和体内连接分子的处理。随后由 Cdc5 进行的超磷酸化似乎降低了 Sgs1 的活性，同时激活了 Mus81-Mms4 和 MutLγ-Exo1。这些发现表明存在一种协同机制，可驱动减数分裂和有丝分裂细胞中非交叉和交叉重组体的有序形成。
