Mutagenic lesion bypass and two functionally different RecA proteins in Deinococcus deserti.

Summary RecA is essential for extreme radiation tolerance in Deinococcus radiodurans. Interestingly, Sahara bacterium Deinococcus deserti has three recA genes (recAC, recAP1, recAP3) that code for two different RecA proteins (RecAC, RecAP). Moreover, and in contrast to other sequenced Deinococcus species, D. deserti possesses homologues of translesion synthesis (TLS) DNA polymerases, including ImuY and DnaE2. Together with a lexA homologue, imuY and dnaE2 form a gene cluster similar to a widespread RecA/LexA-controlled mutagenesis cassette. After having developed genetic tools, we have constructed mutant strains to characterize these recA and TLS polymerase genes in D. deserti. Both RecAC and RecAP are functional and allow D. deserti to survive, and thus repair massive DNA damage, after exposure to high doses of radiation. D. deserti is mutable by UV, which requires ImuY, DnaE2 and RecAC, but not RecAP. RecAC, but not RecAP, facilitates induced expression of imuY and dnaE2 following UV exposure. We propose that the extra recAP1 and recAP3 genes may provide higher levels of RecA protein for efficient error-free repair of DNA damage, without further increasing error-prone lesion bypass by ImuY and DnaE2, whereas limited TLS may contribute to adaptation to harsh conditions by generating genetic variability.