Daza P, Reichenberger S, Göttlich B, Hagmann M, Feldmann E, Pfeiffer P
Institut für Genetik, Universität zu Köln, Germany.
Biol Chem. 1996 Dec;377(12):775-86. doi: 10.1515/bchm3.1996.377.12.775.
DNA end-joining, a process related to illegitimate recombination and capable of rejoining unrelated pairs of DNA ends in the absence of sequence homology, is considered the major pathway of double-strand break (DSB) repair in mammalian cells. Whole cell and nuclear extracts from three human and one mouse cell line were investigated for their capacities to promote nonhomologous DNA end-joining and their relative activities of DNA-PK, a mammalian DNA end-binding protein complex implicated in DSB-repair. The levels of DNA end-joining and the spectra of junctions of the human systems were identical with the ones of a previously described cell-free joining system derived from Xenopus laevis eggs. Due to the presence of potent 3'-5'-exonuclease activities the mouse system displayed decreased levels of DNA end-joining and larger fractions of junctions containing deletions but otherwise the basic mechanisms of junction formation appeared to be identical with the Xenopus system. DNA-PK activity was found to be equally low in the Xenopus and the mouse system but 4- to 6-fold increased in the human systems. Our results suggest that the mechanisms of DNA end-joining may be modulated by the level of exonuclease activities and/or DNA end-protecting factors but are otherwise highly conserved in vertebrate cells.
DNA末端连接是一种与异常重组相关的过程，能够在不存在序列同源性的情况下重新连接不相关的DNA末端对，被认为是哺乳动物细胞中双链断裂（DSB）修复的主要途径。对来自三个人类细胞系和一个小鼠细胞系的全细胞提取物和核提取物进行了研究，以考察它们促进非同源DNA末端连接的能力以及DNA-PK（一种参与DSB修复的哺乳动物DNA末端结合蛋白复合物）的相对活性。人类系统的DNA末端连接水平和连接点谱与先前描述的源自非洲爪蟾卵的无细胞连接系统相同。由于存在有效的3'-5'-外切核酸酶活性，小鼠系统的DNA末端连接水平降低，且含有缺失的连接点比例更大，但连接点形成的基本机制似乎与非洲爪蟾系统相同。发现非洲爪蟾和小鼠系统中的DNA-PK活性同样较低，但在人类系统中增加了4至6倍。我们的结果表明，DNA末端连接机制可能受外切核酸酶活性水平和/或DNA末端保护因子的调节，但在脊椎动物细胞中在其他方面高度保守。
