Study On The Nucleic Acid Helicase In Deinococcus Radiodurans

Deinococcus radiodurans is one of the most radio-resistant organisms. It has an extreme resistance to the stress of y radiation, UV radiation and hydrogen peroxide. D radiodurans can survive a5kGy ionizing radiation with no lethality. Efficient DNA repair mechanism, a variety of antioxidant and rapid DNA damage mechanisms contribute to the extreme radio-resistance of D. radiodurans. DNA and RNA are a pair of twin molecules. The earliest origins of life may come from the "nucleic world", DNA and RNA differentiated later. In life system, Protein, DNA, RNA play a major role and are the troika in living systems. It goes without saying that nucleic acid helicase plays an important role. But in D. radiodurans systematic study nucleic acid helicase articles rarely reported.Deinococcus radiodurans genome encodes18nucleic acid helicase and we selected the only three RNA helicases and three kinds of DNA helicase. They are DR162、DR0335、DRB0135、DRB0136、DR0065、DR1532. We first constructed the knockout mutant strains of the six genes and then investigated the survival rates of these mutant and wildtype strains under the stress of DNA damage agents. We found that the mutation of two genes (drb0136, dr1532) did not effect on the radio-resistance of D. radiodurans, indicating that these two genes had no significant contribution to ionizing radiation resistance and may not involve in regulation of DNA repair mechanisms during PIR. But the other four nucleic acid helicase mutant strains were sensitive to DNA-damaging agents, such as y radiation, UV radiation, and hydrogen peroxide. And dr1624deletion leads Deinococcus radiodurans very sensitive to hydrogen peroxide. To better understand the stress resistance phenotype of the mutant strain, we further studied the antioxidant activity of mutant strains of the six nucleic acid helicases. The results showed that△DR162、△DRB0135mutant strains had the worst capacity of the antioxidant activity. It even showed a4-5times huge difference when compared with the wild-type strain R1. Another RNA helicase mutant strain’s antioxidant activity was also lower than the selected DNA helicase mutant strains. That reflected the RNA helicases played an important role in the Deinococcus radiodurans.Based on the strong sensitive to the hydrogen peroxide of△DR1624, we failed to purify DR1624protein in vitro after changing various of conditions. So we just purified the C-terminus deleted protein. At the same time, we found that the dr1624gene sequences in NCBI may have a mistake. Its N-terminal was shorter than the actual amino acid and frameshift mutation resulted in the early termination of the actual sequence.The present study demonstrates that the nucleic acid helicases, especially RNA helicase involved in the resistance phenotype of Deinococcus radiodurans, but the specific mechanisms need further study.