Molecular Mechanisms of Radiation-Resistance in Deinococcus radiodurans

耐辐射异常球菌是一种革兰氏阳性、红色、非运动性细菌，最初在1957年被鉴定为辐照肉类罐头的污染物。它已在世界各地从富含有机营养素的地方分离出来，如动物粪便和加工肉类。耐辐射D.radiodurans对许多损伤DNA的试剂和条件具有极强的抵抗力，包括电离和紫外线辐射以及过氧化氢。当D.当将抗辐射蛋白暴露于6000戈伊X射线时，超过200个双链面包（DSB）被引入染色体中。DSB不仅被修复而不丧失活力，而且染色体也明显相似，使得基因组的线性连续性不受损伤或修复过程的影响。D. DNA损伤表明1）它们具有增强DNA修复蛋白的常规补体的有效性的能力，或者2）它们采用与其他原核生物根本不同的修复机制。我们的研究结果表明：1）每个细胞至少有4个相同的染色体拷贝; 2）它们不仅具有大肠杆菌的同源基因recA、莱克萨和uvrA，而且还具有几个尚未鉴定的DNA修复基因; 3）它们可以在4小时内从200个或更多的DSB中修复DNA结构，其中recA和未知基因参与了修复过程，以及4）如果监测到5-氟尿嘧啶抗性突变，recA缺陷型菌株具有增变子表型，表明基因组不稳定性的作用。

Deinococcus radiodurans is a Gram-positive, red-pigmented, nonmotile bacterium that was originally identified as a contaminant of irradiated canned meat at 1957. It has been isolated worldwide from locations rich in organic nutrients such as animal feces and processed meat. D.radiodurans is an extremely resistant to a number of agents and conditions that damage DNA, including ionizing and ultraviolet radiation and hydrogen peroxide. When an exponential-phase culture of D. radiodurans is exposed to 6000 Gy x-rays, more than 200 double-strand breads (DSB) are introduced into the chromosome. The DSBs are not only repaired without loss of viability, but the chromosome is also apparently resembled so that the linear continuity of the genomes is unaffected by either the damage or the repair process. The capacity of D. radioudurans to survive.DNA damage suggests that 1)they have the ability to potentiate the effectiveness of the conventional complement of DNA repair proteins, or that 2)they employ repair mechanisms that are fundamentally different from other prokaryotes. Our results indicate that 1)there are at least four identical copies of chromosome per cell, 2)they have not only Escherichia coli homologs for DNA repair, such as the recA, lexA and uvrA, but also several of DNA repair genes which have not been identified, 3)they can restore DNA structure from 200 or more DSBs within 4 hours, and for the processes, recA and unknown genes are involved, and that 4)recA deficient strains have a mutator phenotype if 5-fluorouracil-resistant mutation is monitored, suggesting the role of genome instability.