Identification of the uvrD gene product of Escherichia coli as DNA helicase II and its induction by DNA-damaging agents.

Taking advantage of overproduction of the uvrD protein in cells that harbor multicopy plasmids carrying the uvrD gene, we have purified protein to physical homogeneity. The purified protein possesses single-stranded DNA-dependent ATPase and ATP-dependent DNA unwinding activities, and both activities are equally inactivated by antibodies raised against DNA helicase II. Molecular weight (75,000) and chromatographic properties of the uvrD protein are also similar to those of DNA helicase II and DNA-dependent ATPase I (Richet, E., and Kohiyama, M. (1976) J. Biol. Chem. 251, 808-812; Abdel-Monem, M., Dürwald, H., and Hoffmann-Berling, H. (1977) Eur. J. Biochem. 79, 39-45). Thus, it is concluded that the uvrD protein is identical with DNA helicase II and DNA-dependent ATPase I. Expression of the uvrD gene, as assayed by DNA-dependent ATPase activity, was stimulated by exposure of bacteria to nalidixic acid or mitomycin C. No increase in ATPase activity was observed with recA mutant cells, although basic levels of DNA-dependent ATPase activity in recA+ and recA- strains were almost the same. Thus, the uvrD gene is constitutively expressed but also regulated in a recA-dependent fashion.