Hydrolysis of nucleoside triphosphates catalyzed by the recA protein of Escherichia coli. Hydrolysis of UTP.

Hydrolysis of UTP catalyzed by the recA protein of Escherichia coli is stimulated by both double- (DS) and single-stranded (SS) DNA. DS DNA-dependent UTPase activity has a sharp optimum near pH 6. SS DNA-dependent UTP hydrolysis also is optimal near pH 6, although considerable activity remains at pH 8. Both SS and DS DNA-dependent UTPase activities are nonlinearly dependent on recA protein concentration at pH 6 but the SS DNA-dependent reaction shows a linear dependence on enzyme concentration at pH 8. The Km for UTP in the SS DNA-dependent reaction decreases from 147 microM at pH 8 to 33 microM at pH 6. The Km for UTP in the DS DNA-dependent reaction is 247 microM at pH 6. In addition, the Hill coefficient for UTP in the SS DNA-dependent reaction decreases from 3.5 at pH 8 to 1.9 at pH 6, while in the DS DNA-dependent reaction, the Hill coefficient is 2.4 at pH 6. Thus, the UTPase activity of the recA protein differs from the ATPase activity of recA protein primarily in the pH dependence of KmUTP, Vmax, and response to enzyme concentration of the SS DNA-dependent hydrolysis reaction. These differences may be related to the inability of UTP to substitute effectively for ATP in recA protein-promoted annealing and assimilation of SS DNA.