A possible role of Ku in mediating sequential repair of closely opposed lesions
A possible role of Ku in mediating sequential repair of closely opposed lesions
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DOI：
10.1074/jbc.m010906200
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发表时间：
2001-04-20
影响因子：
4.8
通讯作者：
Kow, YW
中科院分区：
文献类型：
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作者：
Hashimoto, M;Donald, CD;Kow, YW
电离辐射暴露的特征之一是形成包括紧密相对的病变的簇状损伤。我们发现，Ku 70/80复合物（Ku）在修复DNA中紧密相对的损伤中发挥作用。含有接近相对单链断裂的二氢尿嘧啶（DHU）的DNA用作模型底物。发现当底物DNA仅含有DHU时，gu对人核酸内切酶III的酶活性没有影响。然而，对于含有与单链断裂紧密相反的DHU的DNA，Ku抑制人核酸内切酶III的切口活性以及由酶诱导的游离双链断裂的量，发现Ku对自由双链断裂形成的抑制作用远大于Ku对人核酸内切酶III切口活性的抑制作用。此外，当核酸内切酶III存在时，伴随着Ku-DNA复合物形成的增加。用大肠杆菌内切核酸酶III也观察到类似的结果。这些结果表明，Ku通过螯合形成为Ku-DNA复合物的双链断裂来减少核酸内切酶III诱导的游离双链断裂的形成。在这样做时，Ku有助于避免中间游离双链断裂的形成，可能有助于减少可能由明显双链断裂的错接导致的致突变事件。
One of the hallmarks of ionizing radiation exposure is the formation of clustered damage that includes closely opposed lesions. We show that the Ku70/80 complex (Ku) has a role in the repair of closely opposed lesions in DNA. DNA containing a dihydrouracil (DHU) close to an opposing single strand break was used as a model substrate. It was found that gu has no effect on the enzymatic activity of human endonuclease III when the substrate DNA contains only DHU, However, with DNA containing a DHU that is closely opposed to a single strand break, Ku inhibited the nicking activity of human endonuclease III as well as the amount of free double strand breaks induced by the enzyme, The inhibition on the formation of a free double strand break by Ku was found to be much greater than the inhibition of human endonuclease III-nicking activity by Ku, Furthermore, there was a concomitant increase in the formation of Ku-DNA complexes when endonuclease III was present. Similar results were also observed with Escherichia coli endonuclease III. These results suggest that Ku reduces the formation of endonuclease III-induced free double strand breaks by sequestering the double strand breaks formed as a Ku-DNA complex. In doing so, Ku helps to avoid the formation of the intermediary free double strand breaks, possibly helping to reduce the mutagenic event that might result from the misjoining of frank double strand breaks.