Molecular mechanism of extreme DNA damage resistance in Deinococcus spp.

DNA双链断裂是基因组中最致命的损伤形式，如果修复不当，会导致基因丢失和/或染色体重排。造成这种损害的电离辐射源包括宇宙辐射、氡和核武器试验遗留的放射性物质的衰变以及发电过程中产生的乏核燃料。毫不奇怪，对所有形式的生命来说，暴露在这种电离辐射下的可容忍水平是非常小的。一个值得注意的例外是耐辐射球菌。Deinococcus能够承受的电离辐射剂量是人类存活剂量的1500倍，其杀灭大肠杆菌基因组的剂量是人类的10倍[Battista 1997]。值得注意的是，尽管被粉碎成数百个小的DNA片段，耐辐射球菌很容易重新组装一个功能基因组。这一成就归因于多种保护机制的结合，包括多基因组拷贝的存在、特征基因组结构以及已知或新的DNA修复机制。尽管传统的修复机制似乎在耐辐射球菌中是活跃的，但所显示的修复速度和准确性与之前表征的所有途径不一致[Cox 2005]。

DNA Double-strand breaks represent the most lethal form of damage in the genome, resulting in genetic loss and/or chromosomal re-arrangement if not properly repaired. Sources of ionizing radiation (IR) responsible for such damage include cosmic radiation, radon and the decay of radioactive material left over from nuclear weapons testing and spent nuclear fuel generated during power production. Not surprisingly, tolerable levels of exposure to such ionizing radiation are exceedingly small for all forms of life. One notable exception is the bacterium Deinococcus radiodurans. Deinococcus is able to withstand a dose of ionizing radiation 1500 times greater than humans can survive and one that would obliterate the E. coli genome 10 times over [Battista 1997]. Remarkably, despite being shattered into hundreds of small DNA fragments, Deinococcus radiodurans readily reassembles a functional genome. This feat has been attributed to the combination of a number of protective mechanisms including the presence of multiple genome copies, characteristic genome structure, and known or novel DNA repair mechanisms. Although traditional repair mechanisms appear to be active in D. radiodurans, the speed and accuracy of repair displayed are inconsistent with all previously characterized pathways [Cox 2005].