Kajander O A, Karhunen P J, Holt I J, Jacobs H T
Institute of Medical Technology and Tampere University Hospital, FIN-33014 University of Tampere, Finland.
EMBO Rep. 2001 Nov;2(11):1007-12. doi: 10.1093/embo-reports/kve233.
Recombination intermediates containing four-way (Holliday) junctions are generated during DNA repair and replication in many systems, including yeast mitochondrial DNA (mtDNA). In contrast, convincing evidence for recombination in mammalian mtDNA is lacking. We have used two-dimensional agarose-gel electrophoresis to analyse non-linear forms of mtDNA in human heart muscle. Replication intermediates from both the coupled and strand-asynchronous mtDNA replication pathways were detected. An additional class of non-linear molecules, with the electrophoretic properties of four-way junctions, was also prominent. These molecules were insensitive to topoisomerase I or RNase H, but were diminished by branch migration or RuvC treatment. Junctional molecules were detected in all regions of the mitochondrial genome, were found in myocardial DNA from young and old adults, but were present at lower levels in skeletal muscle and placenta. We suggest that they could represent intermediates of mtDNA repair, given their prevalence in the oxyradical-rich environment of heart muscle mitochondria.
在包括酵母线粒体DNA（mtDNA）在内的许多系统中，DNA修复和复制过程中会产生含有四链（霍利迪）连接体的重组中间体。相比之下，哺乳动物mtDNA中重组的令人信服的证据却很缺乏。我们使用二维琼脂糖凝胶电泳来分析人类心肌中mtDNA的非线性形式。检测到了来自偶联和链异步mtDNA复制途径的复制中间体。另一类具有四链连接体电泳特性的非线性分子也很突出。这些分子对拓扑异构酶I或核糖核酸酶H不敏感，但通过分支迁移或RuvC处理会减少。连接分子在线粒体基因组的所有区域都能检测到，在年轻人和老年人的心肌DNA中都有发现，但在骨骼肌和胎盘中的含量较低。鉴于它们在富含氧自由基的心肌线粒体环境中普遍存在，我们认为它们可能代表mtDNA修复的中间体。
