Novel DNA Repair Gene of Radioresistant Bacterium, Deinococcus radiodurans
Issay NARUMI*a, Shigeru KITAYAMAb and Hiroshi WATANABEa
a Biotechnology Laboratory, TRCRE, JAERI, 1233 Watanuki, Takasaki 370-12, Japan
b Cellular Physiology Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-01, Japan
The extraordinary radiation resistance of Deinococcus radiodurans is attributed to its high and accurate capacity for repairing DNA damage induced by chemicals, ultraviolet light and ionizing radiation. Several genes involved in DNA repair have so far been isolated from D. radiodurans in our laboratory. These includes recA, recN, recR, uvrA, uvrC, ruvB, polA and lexA. The existence of these genes means that D. radiodurans has excision and recombination repair pathways, and also SOS regulatory mechanism. However, these genes are ubiquitously distributed among bacteria. Since the predicted amino acid sequences of the genes of D. radiodurans do not differ from those of their Escherichia coli counterparts, the function of each homologous protein is insufficient to account for the extraordinary radiation resistance of D. radiodurans.
By analyzing a radiosensitive mutant, a novel gene "pprA (pleiotropic gene promoting DNA repair)" required for DNA repair was found out. The gene product was expected to have a quite new function. PprA protein was purified from a recombinant E. coli in which the gene had been overexpressed. By Western analysis using anti-PprA, it was found that the expression of pprA was induced when DNA damage occurred in D. radiodurans. The PprA protein could interact with double- stranded DNA but not with single-stranded DNA. This interaction seems to play an important role in the mechanism of extraordinary radioresistance of D. radiodurans.
