ParA proteins of secondary genome elements cross-talk and regulate radioresistance through genome copy number reduction in Deinococcus radiodurans.

Deinococcus radiodurans, an extremely radioresistant bacterium has a multipartite genome system and ploidy. Mechanisms underlying such types of bacterial genome maintenance and its role in extraordinary radioresistance are not known in this bacterium. Chromosome I (Chr I), chromosome II (Chr II) and megaplasmid (Mp) encode its own set of genome partitioning proteins. Here, we have characterized P-loop ATPases of Chr II (ParA2) and Mp (ParA3) and their roles in the maintenance of genome copies and extraordinary radioresistance. Purified ParA2 and ParA3 showed nearly similar polymerization kinetics and interaction patterns with DNA. Electron microscopic examination of purified proteins incubated with DNA showed polymerization on nicked circular dsDNA. ParA2 and ParA3 showed both homotypic and heterotypic interactions to each other, but not with ParA1 (ParA of Chr I). Similarly, ParA2 and ParA3 interacted with ParB2 and ParB3 but not with ParB1 in vivo ParB2 and ParB3 interaction with cis-elements located upstream to the corresponding parAB operon was found to be sequence-specific. Unlike single mutant of parA2 and parA3, their double mutant (ΔparA2ΔParA3) affected copy number of cognate genome elements and resistance to γ-radiation as well as hydrogen peroxide in this bacterium. These results suggested that ParA2 and ParA3 are DNA-binding ATPases producing higher order polymers on DNA and are functionally redundant in the maintenance of secondary genome elements in D. radiodurans The findings also suggest the involvement of secondary genome elements such as Chr II and Mp in the extraordinary radioresistance of D. radiodurans.