減數分裂中MutLγ核酸內切酶調控機制
作者:
小柯機器人發布時間:2020/8/21 14:48:46
瑞士大學(USI)Petr Cejka研究組取得最新進展。他們揭示了減數分裂中MLH1-MLH3(MutLγ)核酸內切酶的調控機制。該研究於2020年8月19日發表於《自然》。
他們生化重構了這種交叉途徑的關鍵要素,顯示人類支撐交叉過程的MSH4-MSH5(MutSγ),其結合分支重組中間體並與MutLγ締合,從而穩定了聯合分子結構和相鄰雙鏈DNA。MutSγ通過MutLγ內切核酸酶直接刺激DNA切割。但只有當存在MutSγ時,EXO1才能進一步刺激MutLγ活性。複製因子C(RFC)和增殖細胞核抗原(PCNA)是核酸酶的其他組成部分,從而觸發了交叉反應。MutLγ不能與PCNA相互作用的釀酒酵母菌株在形成交叉時存在缺陷。
最後,MutLγ–MutSγ–EXO1–RFC–PCNA核酸酶複合物優先切割具有霍利迪連接的DNA,但沒有典型的分辨酶活性。取而代之的是,它可能通過在連接點附近切割雙鏈DNA來加工減數分裂重組中間體。由於MutLγ產生的DNA切口依賴於其輔助因子,因此MutSγ和RFC–PCNA在減數分裂重組中間體上的不對稱分布可能會驅動DNA裂解。MutLγ核酸酶激活的這種模式可能解釋了減數分裂染色體中霍利迪結或其前體的交叉特異性加工。
據介紹,在第一次減數分裂前期,細胞故意破壞其DNA。這些DNA斷裂可通過同源重組得到修復,這有利於適當的染色體分離,並使同源染色體之間的DNA片段相互交換。依賴於MutLγ核酸酶的途徑已通過未知機制參與減數分裂重組中間體向交叉的偏向加工。
附:英文原文
Title: Regulation of the MLH1–MLH3 endonuclease in meiosis
Author: Elda Cannavo, Aurore Sanchez, Roopesh Anand, Lepakshi Ranjha, Jannik Hugener, Cline Adam, Ananya Acharya, Nicolas Weyland, Xavier Aran-Guiu, Jean-Baptiste Charbonnier, Eva R. Hoffmann, Valrie Borde, Joao Matos, Petr Cejka
Issue&Volume: 2020-08-19
Abstract: During prophase of the first meiotic division, cells deliberately break their DNA1. These DNA breaks are repaired by homologous recombination, which facilitates proper chromosome segregation and enables the reciprocal exchange of DNA segments between homologous chromosomes2. A pathway that depends on the MLH1–MLH3 (MutLγ) nuclease has been implicated in the biased processing of meiotic recombination intermediates into crossovers by an unknown mechanism3–7. Here we have biochemically reconstituted key elements of this pro-crossover pathway. We show that human MSH4–MSH5 (MutSγ), which supports crossing over8, binds branched recombination intermediates and associates with MutLγ, stabilizing the ensemble at joint molecule structures and adjacent double-stranded DNA. MutSγ directly stimulates DNA cleavage by the MutLγ endonuclease. MutLγ activity is further stimulated by EXO1, but only when MutSγ is present. Replication factor C (RFC) and the proliferating cell nuclear antigen (PCNA) are additional components of the nuclease ensemble, thereby triggering crossing-over. Saccharomyces cerevisiae strains in which MutLγ cannot interact with PCNA present defects in forming crossovers. Finally, the MutLγ–MutSγ–EXO1–RFC–PCNA nuclease ensemble preferentially cleaves DNA with Holliday junctions, but shows no canonical resolvase activity. Instead, it probably processes meiotic recombination intermediates by nicking double-stranded DNA adjacent to the junction points9. As DNA nicking by MutLγ depends on its co-factors, the asymmetric distribution of MutSγ and RFC–PCNA on meiotic recombination intermediates may drive biased DNA cleavage. This mode of MutLγ nuclease activation might explain crossover-specific processing of Holliday junctions or their precursors in meiotic chromosomes4. Reconstitution of the activation of the MLH1–MLH3 endonuclease shows how crossovers are formed during meiosis.
DOI: 10.1038/s41586-020-2592-2
Source: https://www.nature.com/articles/s41586-020-2592-2