Mitochondrial DNA Replication Group, Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina, USA.
Mitochondrial DNA Replication Group, Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina, USA.
J Biol Chem. 2020 Dec 18;295(51):17802-17815. doi: 10.1074/jbc.RA120.015390.
Faithful replication of the mitochondrial genome is carried out by a set of key nuclear-encoded proteins. DNA polymerase γ is a core component of the mtDNA replisome and the only replicative DNA polymerase localized to mitochondria. The asynchronous mechanism of mtDNA replication predicts that the replication machinery encounters dsDNA and unique physical barriers such as structured genes, G-quadruplexes, and other obstacles. In vitro experiments here provide evidence that the polymerase γ heterotrimer is well-adapted to efficiently synthesize DNA, despite the presence of many naturally occurring roadblocks. However, we identified a specific G-quadruplex-forming sequence at the heavy-strand promoter (HSP1) that has the potential to cause significant stalling of mtDNA replication. Furthermore, this structured region of DNA corresponds to the break site for a large (3,895 bp) deletion observed in mitochondrial disease patients. The presence of this deletion in humans correlates with UV exposure, and we have found that efficiency of polymerase γ DNA synthesis is reduced after this quadruplex is exposed to UV in vitro.
线粒体基因组的忠实复制是由一组关键的核编码蛋白完成的。DNA 聚合酶 γ 是 mtDNA 复制体的核心组成部分，也是唯一定位于线粒体的复制 DNA 聚合酶。mtDNA 复制的异步机制预测，复制机制会遇到双链 DNA 以及独特的物理障碍，如结构基因、G-四联体和其他障碍。这里的体外实验提供了证据，表明聚合酶 γ 三聚体能够很好地适应，尽管存在许多天然的障碍，但仍能有效地合成 DNA。然而，我们在重链启动子 (HSP1) 处鉴定出一个特定的形成 G-四联体的序列，该序列有可能导致 mtDNA 复制的显著停滞。此外，这个 DNA 的结构区域与在患有线粒体疾病的患者中观察到的一个大（3895bp）缺失的断裂点相对应。这种缺失在人类中存在与紫外线暴露有关，我们已经发现，在体外将这个四联体暴露于紫外线后，聚合酶 γ 的 DNA 合成效率会降低。
