The survival fraction of DR0199-null mutant decreased by tenfold after treatment
with 50 mM H2O2, 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 radicaland
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.