RecF protein is one of the important proteins involved in DNA recombination and repair. RecF protein has been shown to bind single-stranded DNA (ssDNA) in the absence of ATP (T. J. Griffin IV and R. D. Kolodner, J. Bacteriol. 172:6291-6299, 1990; M. V. V. S. Madiraju and A. J. Clark, Nucleic Acids Res. 19:6295-6300, 1991). In the present study, using 8-azido-ATP, a photo-affinity analog of ATP, we show that RecF protein binds ATP and that the binding is specific in the presence of DNA. 8-Azido-ATP photo-cross-linking is stimulated in the presence of DNA (both ssDNA and double-stranded DNA [dsDNA]), suggesting that DNA enhances the affinity of RecF protein for ATP. These data suggest that RecF protein possesses independent ATP- and DNA-binding sites. Further, we find that stable RecF protein-dsDNA complexes are obtained in the presence of ATP or ATP-gamma-S [adenosine-5'-O-(3-thio-triphosphate)]. No other nucleoside triphosphates served as necessary cofactors for dsDNA binding, indicating that RecF is an ATP-dependent dsDNA-binding protein. Since a mutation in a putative phosphate-binding motif of RecF protein results in a recF mutant phenotype (S. J. Sandler, B. Chackerian, J. T. Li, and A. J. Clark, Nucleic Acids Res. 20:839-845, 1992), we suggest on the basis of our data that the interactions of RecF protein with ATP, with dsDNA, or with both are physiologically important for understanding RecF protein function in vivo.