The Role of XPG in Processing (CAG)n/(CTG)n DNA Hairpins.
The Role of XPG in Processing (CAG)n/(CTG)n DNA Hairpins.
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DOI：
10.1186/2045-3701-1-11
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发表时间：
2011-03-09
影响因子：
7.5
通讯作者：
Li GM
中科院分区：
文献类型：
--
作者：
Hou C;Zhang T;Tian L;Huang J;Gu L;Li GM
在DNA复制或修复过程中，疾病相关的(CAG)n/(CTG)n扩张可能是由于在新合成的或缺口DNA链的重复段中形成发夹结构而导致的。最近的研究发现了一种缺口导向的(CAG)n/(CTG)n发夹修复(HPR)系统，它通过内切开将(CAG)n/(CTG)n发夹从人类细胞中移除。由于这一过程与XPG和XPF内切酶在核苷酸切除修复过程中去除大量DNA损伤的机制高度相似，因此我们评估了XPG在传导(CAG)n/(CTG)n HPR中的潜在作用。为了确定XPG内切酶是否参与去除(CAG)n/(CTG)n发夹，我们检测了两个XPG缺陷细胞系(GM16024和AG08802)在体外处理(CAG)n/(CTG)n发夹的能力。我们证明，GM16024细胞系处理所有发夹底物的效率与HeLa细胞一样高，而AG08802细胞系在HPR方面存在部分缺陷。对修复中间产物的分析表明，两个XPG缺陷系的核提取液都通过切口去除了CAG/CTG发夹，但切割产物与HeLa提取液产生的产物不同。我们还表明，纯化的重组XPG蛋白通过促进发夹上5‘端的切开，极大地刺激了XPG缺陷提取物中的HPR。我们的结果有力地表明：1)人类细胞有多种途径去除位于新合成(或缺口)DNA链上的(CAG)n/(CTG)n发夹；2)XPG虽然不是去除(CAG)n/(CTG)n发夹所必需的，但通过促进发夹的5‘切开来刺激HPR。这项研究揭示了XPG在基因组维持中的新作用，并表明XPG与三核苷酸重复序列扩张引起的疾病有关。
During DNA replication or repair, disease-associated (CAG)n/(CTG)n expansion can result from formation of hairpin structures in the repeat tract of the newly synthesized or nicked DNA strand. Recent studies identified a nick-directed (CAG)n/(CTG)n hairpin repair (HPR) system that removes (CAG)n/(CTG)n hairpins from human cells via endonucleolytic incisions. Because the process is highly similar to the mechanism by which XPG and XPF endonucleases remove bulky DNA lesions during nucleotide excision repair, we assessed the potential role of XPG in conducting (CAG)n/(CTG)n HPR. To determine if the XPG endonuclease is involved in (CAG)n/(CTG)n hairpin removal, two XPG-deficient cell lines (GM16024 and AG08802) were examined for their ability to process (CAG)n/(CTG)n hairpins in vitro. We demonstrated that the GM16024 cell line processes all hairpin substrates as efficiently as HeLa cells, and that the AG08802 cell line is partially defective in HPR. Analysis of repair intermediates revealed that nuclear extracts from both XPG-deficient lines remove CAG/CTG hairpins via incisions, but the incision products are distinct from those generated in HeLa extracts. We also show that purified recombinant XPG protein greatly stimulates HPR in XPG-deficient extracts by promoting an incision 5' to the hairpin. Our results strongly suggest that 1) human cells possess multiple pathways to remove (CAG)n/(CTG)n hairpins located in newly synthesized (or nicked) DNA strand; and 2) XPG, although not essential for (CAG)n/(CTG)n hairpin removal, stimulates HPR by facilitating a 5' incision to the hairpin. This study reveals a novel role for XPG in genome-maintenance and implicates XPG in diseases caused by trinucleotide repeat expansion.
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DOI：
10.1073/pnas.96.4.1504
发表时间：
1999-02-16
影响因子：
11.1
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1998-10-13
影响因子：
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