While mammalian mitochondria are known to possess a robust base excision repair system, direct evidence for the existence of additional mitochondrial DNA repair pathways is elusive. Herein a PCR-based assay was employed to demonstrate that plasmids containing DNA-protein crosslinks are rapidly repaired following electroporation into isolated mammalian mitochondria. Several lines of evidence argue that this repair occurs via homologous recombination. First, DNA-protein crosslinks present on plasmid DNA homologous to the mitochondrial genome were efficiently repaired (21 % repair in three hours), whereas a DNA-protein crosslink present on DNA that lacked homology to the mitochondrial genome remained unrepaired. Second, DNA-protein crosslinks present on plasmid DNA lacking homology to the mitochondrial genome were repaired when they were co-electroporated into mitochondria with an undamaged, homologous plasmid DNA molecule. Third, no repair was observed when DNA-protein crosslink-containing plasmids were electroporated into mitochondria isolated from cells pre-treated with the Rad51 inhibitor B02. These findings suggest that mitochondria utilize homologous recombination to repair endogenous and xenobiotic-induced DNA-protein crosslinks. Consistent with this interpretation, cisplatin-induced mitochondrial DNA-protein crosslinks accumulated to higher levels in cells pre-treated with B02 than in control cisplatin-treated cells. These results represent the first evidence of how spontaneous and xenobiotic-induced DNA-protein crosslinks are removed from mitochondrial DNA.

虽然已知哺乳动物线粒体具有强大的碱基切除修复系统，但存在额外线粒体 DNA 修复途径的直接证据是难以捉摸的。在本文中，基于 PCR 的测定被用来证明含有 DNA-蛋白质交联的质粒在电穿孔到分离的哺乳动物线粒体后被快速修复。几条证据表明，这种修复是通过同源重组。首先，与线粒体基因组同源的质粒 DNA 上存在的 DNA-蛋白质交联得到有效修复（三小时内修复 21%），而与线粒体基因组缺乏同源性的 DNA 上存在的 DNA-蛋白质交联仍未修复。其次，与线粒体基因组缺乏同源性的质粒 DNA 上存在的 DNA-蛋白质交联被修复，当它们与未损坏的同源质粒 DNA 分子共同电穿孔进入线粒体时。第三，当含有 DNA-蛋白质交联的质粒被电穿孔到从用 Rad51 抑制剂 B02 预处理的细胞分离的线粒体中时，没有观察到修复。这些发现表明线粒体利用同源重组来修复内源性和外源性诱导的 DNA-蛋白质交联。与这种解释一致，顺铂诱导的线粒体 DNA-蛋白质交联在用 B02 预处理的细胞中比在对照顺铂处理的细胞中积累到更高的水平。这些结果代表了如何从线粒体 DNA 中去除自发和异生物质诱导的 DNA-蛋白质交联的第一个证据。