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Ctp1在减数分裂DNA双链断裂修复早期步骤中的两种可分离功能。

Two separable functions of Ctp1 in the early steps of meiotic DNA double-strand break repair.

作者信息

Ma Lijuan, Milman Neta, Nambiar Mridula, Smith Gerald R

机构信息

Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.

Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA

出版信息

Nucleic Acids Res. 2015 Sep 3;43(15):7349-59. doi: 10.1093/nar/gkv644. Epub 2015 Jun 30.

Abstract

Meiotic programmed DNA double-strand break (DSB) repair is essential for crossing-over and viable gamete formation and requires removal of Spo11-oligonucleotide complexes from 5' ends (clipping) and their resection to generate invasive 3'-end single-stranded DNA (resection). Ctp1 (Com1, Sae2, CtIP homolog) acting with the Mre11-Rad50-Nbs1 (MRN) complex is required in both steps. We isolated multiple S. pombe ctp1 mutants deficient in clipping but proficient in resection during meiosis. Remarkably, all of the mutations clustered in or near the conserved CxxC or RHR motif in the C-terminal portion. The mutants tested, like ctp1Δ, were clipping-deficient by both genetic and physical assays-. But, unlike ctp1Δ, these mutants were recombination-proficient for Rec12 (Spo11 homolog)-independent break-repair and resection-proficient by physical assay. We conclude that the intracellular Ctp1 C-terminal portion is essential for clipping, while the N-terminal portion is sufficient for DSB end-resection. This conclusion agrees with purified human CtIP resection and endonuclease activities being independent. Our mutants provide intracellular evidence for separable functions of Ctp1. Some mutations truncate Ctp1 in the same region as one of the CtIP mutations linked to the Seckel and Jawad severe developmental syndromes, suggesting that these syndromes are caused by a lack of clipping at DSB ends that require repair.

摘要

减数分裂程序性DNA双链断裂(DSB)修复对于交叉互换和形成有活力的配子至关重要,并且需要从5'末端去除Spo11 - 寡核苷酸复合物(剪切)并对其进行切除以产生侵入性的3'末端单链DNA(切除)。在这两个步骤中都需要Ctp1(Com1、Sae2、CtIP同源物)与Mre11 - Rad50 - Nbs1(MRN)复合物共同作用。我们分离出了多个粟酒裂殖酵母ctp1突变体,这些突变体在减数分裂期间剪切功能缺陷但切除功能正常。值得注意的是,所有突变都聚集在C末端部分保守的CxxC或RHR基序中或其附近。所测试的突变体,如ctp1Δ,通过遗传和物理分析均表现出剪切缺陷。但是,与ctp1Δ不同的是,这些突变体对于Rec12(Spo11同源物)非依赖性的断裂修复具有重组能力,并且通过物理分析显示切除功能正常。我们得出结论,细胞内Ctp1的C末端部分对于剪切至关重要,而N末端部分对于DSB末端切除就足够了。这个结论与纯化的人类CtIP切除和内切酶活性相互独立是一致的。我们的突变体为Ctp1的可分离功能提供了细胞内证据。一些突变在与与Seckel和Jawad严重发育综合征相关的CtIP突变之一相同的区域截断了Ctp1,这表明这些综合征是由需要修复的DSB末端缺乏剪切引起的。

https://cdn.ncbi.nlm.nih.gov/pmc/blobs/dbb3/4551917/7a20068dd067/gkv644fig1.jpg

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