The Effects of recQ, uvrD, and recD Mutants of Deinococcus radiodurans on Resistance to DNA Damaging Agents

The genes encoding the putative nuclease RecD and the helicase RecQ were deleted from Deinococcus radiodurans R1 and replaced with constructs conferring hygromycin or spectinomycin resistance. The ÄrecD and ÄrecQ strains were found to be similar to wild type R1 strain in resistance to gamma irradiation. In contrast to the single mutant strains, the ÄuvrD, ÄrecQ double mutant was found to be extremely radiation sensitive, indicating that these proteins share a complementary activity needed for radioresistance. ÄrecD mutants have higher transformation efficiencies than the wild type R1 strains, suggesting an association of RecD with nucleases that degrade single stranded DNA. Mitomycin C and ultraviolet light, DNA damaging agents that generate different patterns of DNA damage relative to ionizing radiation, were also used to induce damage in the wild type strain mutant strains. The ÄuvrD, ÄrecQ double mutant exhibited the highest sensitivity to these mutagens, reiterating that RecQ and UvrD have overlapping activities. Hydrogen peroxide increased the sensitivity of the RecQ mutant approximately ten fold, suggesting that RecFOR protein complex may be important in repairing damage mediated by oxygen radicals.