Ganesh A, North P, Thacker J
Cell and Molecular Biology Division, MRC Radiobiology Unit, Didcot, Oxon, UK.
Mutat Res. 1993 May;299(3-4):251-9. doi: 10.1016/0165-1218(93)90101-i.
The rejoining by human cell extracts of a double-strand break induced by endonuclease treatment at one of several sites within a small DNA molecule was studied. Rejoining was found at each of 8 sites tested, but the rejoin efficiency varied with the nature of the break (e.g., breaks with cohesive ends were rejoined more efficiently than blunt-ended breaks). Extracts from primary and immortalized cell lines, as well as those from individuals with ataxia telangiectasia (A-T), showed the same pattern of relative rejoin efficiencies. However, mis-rejoining varied with the cell extract used, and was particularly elevated with two immortalized A-T cell lines. Mixing experiments showed that the mis-rejoining property of extracts could act in a semi-dominant fashion, depending on the individual efficiencies of the component extracts. The mis-rejoin mechanism involved deletion at sites of short direct repeats at various distances from the initial break site. A model of deletion formation (the strand-exposure and repair model) is restated to explain the sequence repeat dependence found, and is compared to models of homologous DNA recombination.
研究了人类细胞提取物对小DNA分子内几个位点之一经核酸内切酶处理诱导产生的双链断裂的重新连接情况。在所测试的8个位点中的每一个都发现了重新连接，但重新连接效率因断裂的性质而异（例如，具有粘性末端的断裂比平端断裂更有效地重新连接）。原代细胞系和永生化细胞系的提取物，以及共济失调毛细血管扩张症（A-T）患者的提取物，都显示出相同的相对重新连接效率模式。然而，错误重新连接因所用的细胞提取物而异，并且在两种永生化A-T细胞系中特别升高。混合实验表明，提取物的错误重新连接特性可以以半显性方式起作用，这取决于组分提取物的个体效率。错误重新连接机制涉及在距初始断裂位点不同距离处的短直接重复序列位点的缺失。重新阐述了缺失形成模型（链暴露和修复模型）以解释所发现的序列重复依赖性，并与同源DNA重组模型进行了比较。
