DdrB stimulates single-stranded DNA annealing and facilitates RecA-independent DNA repair in Deinococcus radiodurans.

The bacterium Deinococcus radiodurans can survive extremely high exposure to ionizing radiation. The repair mechanisms involved in this extraordinary ability are still being investigated. ddrB is one gene that is highly up-regulated after irradiation, and it has been proposed to be involved in RecA-independent repair in D. radiodurans. Here we cloned, expressed and characterized ddrB in order to define its roles in the radioresistance of D. radiodurans. DdrB preferentially binds to single-stranded DNA. Moreover, it interacts directly with single-stranded binding protein of D. radiodurans DrSSB, and stimulates single-stranded DNA annealing even in the presence of DrSSB. The post-irradiation DNA repair kinetics of a ddrB/recA double mutant were compared to ddrB and recA single mutants by pulsed-field gel electrophoresis (PFGE). DNA fragment rejoining in the ddrB/recA double mutant is severely compromised, suggesting that DdrB-mediated single-stranded annealing plays a critical role in the RecA-independent DNA repair of D. radiodurans.

Xu G ，Lu H ，Wang L ，Chen H ，Xu Z ，Hu Y ，Tian B ，Hua Y ... -  《-》

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》

Role of RecA in DNA damage repair in Deinococcus radiodurans.

Schlesinger DJ 《FEMS MICROBIOLOGY LETTERS》

The deinococcal DdrB protein is involved in an early step of DNA double strand break repair and in plasmid transformation through its single-strand annealing activity.

The Deinococcus radiodurans bacterium exhibits an extreme resistance to ionizing radiation. Here, we investigated the in vivo role of DdrB, a radiation-induced Deinococcus specific protein that was previously shown to exhibit some in vitro properties akin to those of SSB protein from Escherichia coli but also to promote annealing of single stranded DNA. First we report that the deletion of the C-terminal motif of the DdrB protein, which is similar to the SSB C-terminal motif involved in recruitment to DNA of repair proteins, did neither affect cell radioresistance nor DNA binding properties of purified DdrB protein. We show that, in spite of their different quaternary structure, DdrB and SSB occlude the same amount of ssDNA in vitro. We also show that DdrB is recruited early and transiently after irradiation into the nucleoid to form discrete foci. Absence of DdrB increased the lag phase of the extended synthesis-dependent strand annealing (ESDSA) process, affecting neither the rate of DNA synthesis nor the efficiency of fragment reassembly, as indicated by monitoring DNA synthesis and genome reconstitution in cells exposed to a sub-lethal ionizing radiation dose. Moreover, cells devoid of DdrB were affected in the establishment of plasmid DNA during natural transformation, a process that requires pairing of internalized plasmid single stranded DNA fragments, whereas they were proficient in transformation by a chromosomal DNA marker that integrates into the host chromosome through homologous recombination. Our data are consistent with a model in which DdrB participates in an early step of DNA double strand break repair in cells exposed to very high radiation doses. DdrB might facilitate the accurate assembly of the myriad of small fragments generated by extreme radiation exposure through a single strand annealing (SSA) process to generate suitable substrates for subsequent ESDSA-promoted genome reconstitution.

Bouthier de la Tour C ，Boisnard S ，Norais C ，Toueille M ，Bentchikou E ，Vannier F ，Cox MM ，Sommer S ，Servant P ... -  《-》

Single Strand Annealing Plays a Major Role in RecA-Independent Recombination between Repeated Sequences in the Radioresistant Deinococcus radiodurans Bacterium.

Ithurbide S ，Bentchikou E ，Coste G ，Bost B ，Servant P ，Sommer S ... -  《PLoS Genetics》