Recognition of DNA damage and induction of repair proteins in deinococcus radiodurans

In Escherichia coli, the inducible DNA repair system (the SOS system) is regulated by two key proteins; RecA and LexA. Although SOS-like processes have been documented in a wide variety of eubacterial species. The involvement of RecA and LexA in the SOS response is poorly understood in Deinococcus radiodurans. As expression of the deinococcal recA is enhanced after irradiation, the recA seems to be a member of a DNA damage response regulon in D. radiodurans. By investigating the function of deinococcal proteins, we found that LexA is not involved in the regulation of RecA in D. radiodurans. This led us to speculate that D. radiodurans has an alternative DNA damage response mechanism with which to control recA expression. We discovered that a novel protein regulates the expression of recA. The novel regulatory protein (designated PprI) also controls the induction of pprA following irradiation. We also found that the co-protease activity rather than recombination activity of RecA contributes to the radiation resistance in D. radiodurans. The D. radiodurans genome encodes a second but diverged copy of LexA (designated LexA2). Analysis of LexA2 indicated that still-unknown repair gene are down-regulated by LexA2. Thus, D. radiodurans possesses unique mechanisms of DNA damage recognition and repair gene induction. (author)