DNA-dependent ATPase, stimulated equally by ss- and dsDNA. Has both ATPase and helicase activities, and translocates along ssDNA displacing bound streptavidin. Its essentiality for growth does not depend on its helicase activity. ATP + H2O = ADP + H(+) + phosphate kcat is 0.035 sec(-1) with ATP. Essential for growth; the 100 C-terminal residues are not required for growth. Belongs to the helicase family. UvrD subfamily.