Microhomology-mediated DNA strand annealing and elongation by human DNA polymerases λ and β on normal and repetitive DNA sequences
Microhomology-mediated DNA strand annealing and elongation by human DNA polymerases λ and β on normal and repetitive DNA sequences
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DOI：
10.1093/nar/gks186
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发表时间：
2012-07-01
影响因子：
14.9
通讯作者：
Huebscher, Ulrich
中科院分区：
文献类型：
--
作者：
Crespan, Emmanuele;Czabany, Tibor;Huebscher, Ulrich
“经典”非同源末端连接（NHEJ）依赖于Ku70/80和DNA连接酶IV/XRCC4复合物，对DNA双链断裂的修复至关重要。真核细胞还具有一种独立于Ku和DNA连接酶4/XRCC4的微同源介导的末端连接（MMEJ）机制。MMEJ机制的组成在很大程度上仍然是未知的。X家族DNA聚合酶（pols）参与了经典的NHEJ途径。我们在本工作中比较了人类家族X DNA pol β， lambda和mu促进不同末端微同源区模型模板的MMEJ的能力。我们的研究结果表明，在没有辅助因子的情况下，DNA pol lambda和DNA连接酶I足以促进体外MMEJ对断裂DNA末端的有效修复。然而，DNA pol β比lambda更有效地促进含有人类亨廷顿基因（CAG）n三联体重复序列的DNA末端的MMEJ，导致三联体扩增。检查点复合体Rad9/Hus1/Rad1促进非重复序列上DNA pol lambda的末端连接，而限制DNA pol beta的三元组扩展。我们提出DNA pol β在MMEJ中可能的新作用，促进（CAG）三联体重复序列的不稳定性。
'Classical' non-homologous end joining (NHEJ), dependent on the Ku70/80 and the DNA ligase IV/XRCC4 complexes, is essential for the repair of DNA double-strand breaks. Eukaryotic cells possess also an alternative microhomology-mediated end-joining (MMEJ) mechanism, which is independent from Ku and DNA ligase 4/XRCC4. The components of the MMEJ machinery are still largely unknown. Family X DNA polymerases (pols) are involved in the classical NHEJ pathway. We have compared in this work, the ability of human family X DNA pols beta, lambda and mu, to promote the MMEJ of different model templates with terminal microhomology regions. Our results reveal that DNA pol lambda and DNA ligase I are sufficient to promote efficient MMEJ repair of broken DNA ends in vitro, and this in the absence of auxiliary factors. However, DNA pol beta, not lambda, was more efficient in promoting MMEJ of DNA ends containing the (CAG)n triplet repeat sequence of the human Huntingtin gene, leading to triplet expansion. The checkpoint complex Rad9/Hus1/Rad1 promoted end joining by DNA pol lambda on non-repetitive sequences, while it limited triplet expansion by DNA pol beta. We propose a possible novel role of DNA pol beta in MMEJ, promoting (CAG)n triplet repeats instability.