Molecular Mechanisms of Radiation-Resistance in Deinococcus radiodurans

耐辐射球菌是一种革兰氏阳性、红色素、不活动的细菌，1957年最初被鉴定为辐照罐头肉的污染物。它已从世界各地富含有机营养的地方分离出来，如动物粪便和加工肉类。耐辐射金黄色葡萄球菌对许多破坏DNA的试剂和条件都具有极强的抵抗力，包括电离、紫外线辐射和过氧化氢。当耐辐射金黄色葡萄球菌的指数期培养受到6000GyX射线照射时，200多个双链面包(DSB)被引入到染色体中。DSB不仅被修复而不会丧失活力，而且染色体也明显相似，因此基因组的线性连续性不受损伤或修复过程的影响。放射线球菌的生存能力。DNA损伤表明，1)它们有能力增强传统DNA修复蛋白的有效性，或者2)它们使用与其他原核生物根本不同的修复机制。我们的结果表明：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DNA修复同源基因，如recA、lexA和uvrA，而且还有一些尚未鉴定的DNA修复基因；3)它们可以在4小时内从200个或更多的DSB中恢复DNA结构，并涉及到recA和未知基因；4)如果监测到5-氟尿嘧啶耐药突变，recA缺陷菌株具有突变子表型，这表明基因组不稳定的作用。

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.