Function Of The Deinococcus Radiodurans SbcD Gene In The Extremely Resistant Mechanism

The extremely radiation resistant bacterium Deinococcus radiodurans was first isolated in 1956 from gamma-irradiated meat. It is extremely resistant to ionizing radiation, ultraviolet, hydrogen peroxide and many other agents that damage DNA. This remarkable range of resistance has been attributed to efficient DNA repair processes. There are lots of research on the DNA repair pathways, including excision repair, direct reversal of damage, nucleotide excision repair , mismatch repair , recombination repair , SOS and so on, and the genome sequence of D. radiodurans wild type strain R1 was already done in 1999.Though lots of research on the structure characteristics and the biochemical mechanism of many key repair genes had been done already, the unique molecular defense mechanism and the accurate regulatory network of DNA repair in Deinococcus radiodurans still remained unknown.Based on the result of bioinformation and amino acid alignment, we found the SbcD (DR1921) and SbcC (DR1922) which make up of the DRSbcCD complex are both belong to the MR protein family. They share the same organizational arrangement with these MR proteins such as bacteriophage T4, E. coli, eukaryotes and archaebacteria. In eukaryotes, MRE11 is the orthologs of SbcD in bacteria. Due to the research of MRE11 in yeast and human, the results show that the MRE11 gene plays an important role in the stability of the genome and has a relativity to the development of cancer. In bacteria, SbcD as an important protein factor participate in the DNA recombination and repair system. In E. coli, the SbcCD complex has hairpin endonuclease activity and can removes protein from a protein-bound DNA end. Compared the genes participate in initiation of recombination repair in E. coli, the RecBC pathway which take charge of the DSBs repair recombination is missing. So there are only SbcCD and/or RecFOR pathways to initiate recombination and the SbcCD complex may play a key role in recombination to repair DSBs and other DNA damages in D. radiodurans.Based on the modern bioinformation method, this study discussed the locus of SbcD (DR1921) in the chromosome, the sequence alignment of different domains and the prediction of biochemical function. In order to study the function of DNA repair mechanism and the oxidation resistant system of D. radioudurans sbcD, we constructed a D. radiodurans sbcD mutant using insert mutagenesis. Then we characterize some phenotype of mutant sbcD. The mutant strain sbcD was sensitive to gamma radiation, hydrogen peroxide and UV than that of wild type strain R1 .The further studies of growth dynamics, genome repair dynamics and activity of antioxidant enzymes showed that D. radioudurans SbcD as a crucial protein of maintain the stability of genome play an important role in the DNA repair mechanism.