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，如果不适当修复，会导致遗传损失和/或染色体重排。造成这种损害的电离辐射(IR)来源包括宇宙辐射、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，对于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都非常小。一个值得注意的例外是耐辐射球菌。变形球菌能够承受比人类生存能力大1500倍的电离辐射，而这种电离辐射将使大肠杆菌基因组消失10倍(Battista 1997)。值得注意的是，尽管耐辐射球菌被分解成数百个小DNA片段，但它很容易重新组装成一个功能正常的基因组。这一成就归因于多种保护机制的结合，包括多个基因组拷贝的存在，特有的基因组结构，以及已知或新颖的DNA修复机制。尽管传统的修复机制似乎在耐辐射金黄色葡萄球菌中是活跃的，但修复的速度和准确性与所有先前描述的途径不一致(COX 2005)。 我们研究的目标是了解参与DNA修复的未鉴定蛋白质如何发挥功能，使耐辐射葡萄球菌具有惊人的DNA修复能力。了解用于抵抗极端IR损伤的DNA修复策略不仅从科学角度来看令人着迷，而且具有巨大的实用潜力。在核燃料加工过程中产生的放射性污染环境中产生的毒素的生物修复方面，耐药球菌很有兴趣[Appukuttan，2006]。此外，NASA正在探索这些生物，希望最终利用获得的信息，在长时间的太空旅行中加强对宇宙辐射的保护。

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]. The goal of our research is to understand how uncharacterized proteins, implicated in DNA repair, function to permit the amazing DNA repair capabilities of Deinococcus radiodurans. Understanding the DNA repair strategies utilized to resist extreme IR damage is not only fascinating from a scientific point of view, but also carries great potential for practical utility. Deinococci are of interest for application in bioremediation of toxins from radioactive contaminated environments generated through processing of nuclear fuel [Appukuttan 2006]. In addition, NASA is exploring these organisms with the idea of eventually using information gained to increase protection form cosmic radiation during prolonged space travel.