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
Vidya A
VA
Molecular Biology Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.
Misra
Hari S
HS
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D004260:DNA Repair / Q000235:genetics / Q000528:radiation effects*; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D034301:Deinococcus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects*; D003851:Deoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D004706:Endodeoxyribonucleases / Q000378:metabolism*; D005720:Gamma Rays; D011836:Radiation Tolerance; D017384:Sequence Deletion; D012996:Solutions
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C061563:SbcC protein, Bacteria; D012996:Solutions; D003851:Deoxyribonucleases; D004706:Endodeoxyribonucleases; D045643:DNA Repair Enzymes