摘要
Base excision repair (BER) corrects a variety of small base lesions in DNA. The UNG gene encodes both the nuclear (UNG2) and the mitochondrial (UNG1) forms of the human uracil-DNA glycosylase (UDG). We prepared mitochondrial extracts free of nuclear BER proteins from human cell lines. Using these extracts we show that UNG is the only detectable UDG in mitochondria, and mitochondrial BER (mtBER) of uracil and AP sites occur by both single-nucleotide insertion and long-patch repair DNA synthesis. Importantly, extracts of mitochondria carry out repair of modified AP sites which in nuclei occurs through long-patch BER. Such lesions may be rather prevalent in mitochondrial DNA because of its proximity to the electron transport chain, the primary site of production of reactive oxygen species. Furthermore, mitochondrial extracts remove 5′ protruding flaps from DNA which can be formed during long-patch BER, by a “flap endonuclease like” activity, although flap endonuclease (FEN1) is not present in mitochondria. In conclusion, combined short- and long-patch BER activities enable mitochondria to repair a broader range of lesions in mtDNA than previously known.
摘要译文
碱基切除修复（BER）纠正DNA中的各种小基底病变。 UNG基因编码人尿嘧啶-DNA糖基化酶（UDG）的核（UNG2）和线粒体（UNG1）形式。我们从人类细胞系中制备了不含核BER蛋白的线粒体提取物。使用这些提取物，我们显示UNG是线粒体中唯一可检测到的UDG，和尿嘧啶和AP位点的线粒体BER（mtBER）通过单核苷酸插入和长补丁修复DNA合成发生。重要的，线粒体提取物通过长距离BER进行核内发生修饰的AP位点的修复。这种损伤在线粒体DNA中可能相当普遍，因为它靠近电子传递链，即活性氧产生的主要部位。此外，线粒体提取物通过“瓣内切核酸酶样”活性从在长贴片BER期间可能形成的DNA中移除5''''突出的皮瓣，尽管瓣内切核酸酶（FEN1）不存在于线粒体中。结论是，结合短和长补丁BER活动使线粒体能够修复比先前已知的更广泛的线粒体DNA损伤。
MansourAkbari;TorkildVisnes;Hans E.Krokan;MaritOtterlei;. Mitochondrial base excision repair of uracil and AP sites takes place by single-nucleotide insertion and long-patch DNA synthesis[J]. DNA Repair, 2008,7(4): 605-616