Genetic and biochemical characteristics of the histone-like protein DR0199 in Deinococcus radiodurans.

Bacterial histone-like proteins are important for nucleoid structure, cell growth, DNA replication, recombination and gene regulation. In this study, we focused on the role of DR0199 (the EbfC orthologue), a newly identified member of the nucleoid-associated protein family in Deinococcus radiodurans. The survival fraction of DR0199-null mutant decreased by tenfold after treatment with 50 mM H(2)O(2), nearly sixfold at a 10 kGy dose of gamma ray and nearly eightfold at a UV exposure of 1000 J m(-2) compared with wild-type cells. The results of fluorescence labelling assays indicated that DR0199 protein localized in the nucleoid area of cells. Electrophoretic mobility shift assays demonstrated that D. radiodurans DR0199 is a DNA-binding protein. Furthermore, DNA protection assays suggested that DR0199 shields DNA from hydroxyl radical- and DNase I-mediated cleavage. The supercoiling of relaxed plasmid DNA in the presence of topoisomerase I revealed that DR0199 constrains DNA supercoils in vitro. Collectively, these findings suggest that DR0199 is a protein with DNA-protective properties and histone-like features that are involved in protecting D. radiodurans DNA from damage.