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PCNA激活MutLγ核酸内切酶以促进减数分裂
2020-08-21 19:23

美国加州大学戴维斯分校Neil Hunter团队发现,PCNA激活MutLγ核酸内切酶以促进减数分裂。该项研究成果于2020年8月19日在线发表在《自然》杂志上。

据研究人员介绍,在减数分裂过程中,交叉重组连接同源染色体以指导它们的精确分离。交叉缺陷会导致不育、流产和先天性疾病。因此,每一对染色体通过指定然后实现高效率杂交的过程获得至少一个交叉。在DNA层面上,交叉是通过dHJ( double-Holliday Junction)中间体的形成和偏向解离。交叉实现的中心原则是,通过将核酸酶切口靶向特定的DNA链,两个HJ在相对的平面中分离。MutLγ复合物的核酸内切酶活性与交叉有关,但是激活和指导链特异性切割的机制仍然未知。

研究人员发现,滑动钳PCNA对于交叉的偏向解离很重要。用人类酶进行的体外测定显示,hPCNA及其装载物hRFC足以激活hMutLγ核酸内切酶。在这种情况下,hMutLγ被交叉因子hEXO1和hMutSγ的共同依赖活性进一步刺激,后者与HJ结合。hMutLγ还特异性结合包括HJ在内的各种分支DNA,但是未观察到经典的解离酶活性,这暗示着核酸内切酶切入连接分支点附近会影响解离。在体内,研究人员发现出芽酵母RFC促进了MutLγ依赖性交叉。此外,PCNA沿着联会染色体定位到预期的交叉位点。

这些数据突出了交叉解离与DNA错配修复的起始步骤之间的相似性,并为减数分裂过程中的交叉特异性dHJ解离建立了新模型。

附:英文原文

Title: PCNA activates the MutLγ endonuclease to promote meiotic crossing over

Author: Dhananjaya S. Kulkarni, Shannon N. Owens, Masayoshi Honda, Masaru Ito, Ye Yang, Mary W. Corrigan, Lan Chen, Aric L. Quan, Neil Hunter

Issue&Volume: 2020-08-19

Abstract: During meiosis, crossover recombination connects homologous chromosomes to direct their accurate segregation1. Defective crossing over causes infertility, miscarriage and congenital disease. Accordingly, each pair of chromosomes attains at least one crossover through processes that designate and then implement crossing over with high efficiency. At the DNA level, crossing over is implemented through the formation and biased resolution of double-Holliday Junction (dHJ) intermediates2,3. A central tenet of crossover resolution is that the two Holliday junctions (HJs) are resolved in opposite planes by targeting nuclease incisions to specific DNA strands4. The endonuclease activity of the MutLγ complex has been implicated in crossover-biased resolution5–10, but mechanisms that activate and direct strand-specific cleavage remain unknown. Here we show that the sliding clamp, PCNA, is important for crossover-biased resolution. In vitro assays with human enzymes reveal that hPCNA and its loader hRFC are sufficient to activate the hMutLγ endonuclease. In this context, hMutLγ is further stimulated by a co-dependent activity of pro-crossover factors hEXO1 and hMutSγ, the latter of which binds HJs11. hMutLγ also specifically binds a variety of branched DNAs, including HJs, but canonical resolvase activity is not observed implying that the endonuclease incises adjacent to junction branch points to effect resolution. In vivo, we show that budding yeast RFC facilitates MutLγ-dependent crossing over. Furthermore, PCNA localizes to prospective crossover sites along synapsed chromosomes. These data highlight similarities between crossover-resolution and the initiation steps of DNA mismatch repair12,13 and evoke a novel model for crossover-specific dHJ resolution during meiosis.

DOI: 10.1038/s41586-020-2645-6

Source: https://www.nature.com/articles/s41586-020-2645-6

Nature:《自然》,创刊于1869年。隶属于施普林格·自然出版集团,最新IF:69.504
官方网址:http://www.nature.com/
投稿链接:http://www.nature.com/authors/submit_manuscript.html


本期文章:《自然》:Online/在线发表

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