The SbcCD complex of Deinococcus radiodurans contributes to radioresistance and DNA strand break repair in vivo and exhibits Mre11-Rad50 type activity in vitro.

Deinococcus radiodurans lacks a homologue of the recB and recC genes, and the sbcA/B genes, of Escherichia coli. Thus, DNA strand break repair in Deinococcus proceeds by pathways that do not utilize these proteins. Unlike E. coli, the absence of recBC and sbcA/sbcB, and presence of only sbcC and sbcD in Deinococcus, indicates an enigmatic role of SbcCD in this bacterium. Studies on sbcCD mutation in Deinococcus showed nearly a 100-fold increase in gamma radiation sensitivity as compared to wild type. The mutant showed a higher rate of in vivo DNA degradation during the post-irradiation recovery period that corresponds to the RecA-dependent DSB repair phase. These cells showed a typical NotI pattern of DNA reassembly during the early phase of DSB repair, but were defective for the subsequent RecA-dependent phase II of DSB repair. Hydrogen peroxide had no effect on cell survival of the mutant. While its tolerance to higher doses of UVC and mitomycin C was significantly decreased as compared to wild type. Purified recombinant SbcCD proteins showed single-stranded endonuclease and 3'-->5' double-stranded DNA exonuclease activities similar to that of the Mre11-Rad50 complex, which is required for DNA strand break repair in higher organisms. These results suggested that the Mre11-Rad50 type nuclease activity of SbcCD proteins contributes to the radiation resistance of D. radiodurans perhaps by promoting the RecA-dependent DSB repair required for polyploid genome maturation.

Kamble VA ，Misra HS 《-》

Additive effects of SbcCD and PolX deficiencies in the in vivo repair of DNA double-strand breaks in Deinococcus radiodurans.

Bentchikou E ，Servant P ，Coste G ，Sommer S ... -  《-》

An exonuclease I-sensitive DNA repair pathway in Deinococcus radiodurans: a major determinant of radiation resistance.

Misra HS ，Khairnar NP ，Kota S ，Shrivastava S ，Joshi VP ，Apte SK ... -  《MOLECULAR MICROBIOLOGY》

Characterization of a DNA damage-inducible membrane protein kinase from Deinococcus radiodurans and its role in bacterial radioresistance and DNA strand break repair.

Deinococcus radiodurans mutant lacking pyrroloquinoline-quinone (PQQ) synthesis shows sensitivity to γ-rays and impairment of DNA double strand break repair. The genome of this bacterium encodes five putative proteins having multiple PQQ binding motifs. The deletion mutants of corresponding genes were generated, and their response to DNA damage was monitored. Only the Δdr2518 mutant exhibited higher sensitivity to DNA damage. Survival of these cells decreased by 3-log cycle both at 6 kGy γ-rays and 1200 Jm(-2) UV (254 nm) radiation, and 2.5-log cycle upon 14 days desiccation at 5% humidity. The Δdr2518 mutant showed complete inhibition of DSB repair until 24 h PIR and disappearance of a few phosphoproteins. The Δdr2518pqqE:cat double mutant showed γ-ray sensitivity similar to Δdr2518 indicating functional interaction of these genes in D. radiodurans. DR2518 contains a eukaryotic type Ser/Thr kinase domain and structural topology suggesting stress responsive transmembrane protein. Its autokinase activity in solution was stimulated by nearly threefold with PQQ and twofold with linear DNA, but not with circular plasmid DNA. More than 15-fold increase in dr2518 transcription and several-fold enhanced in vivo phosphorylation of DR2518 were observed in response to γ irradiation. These results suggest that DR2518 as a DNA damage-responsive protein kinase plays an important role in radiation resistance and DNA strand break repair in D. radiodurans.

Rajpurohit YS ，Misra HS 《-》

RecBC enzyme overproduction affects UV and gamma radiation survival of Deinococcus radiodurans.

Khairnar NP ，Kamble VA ，Misra HS 《-》