Effect of recA protein on the DNAse activities of the recBC enzyme

In Escherichia coli, the recBC enzyme is required for several cellular functions including recombination proficiency, UV resistance, and DNA breakdown following radiation damage to the chromosome, all of which appear to be also under the control of the recA gene. We have studied the influence of purified recA protein on the various nucleolytic activities of the recBC enzyme. Conditions were chosen (with GTP as nucleoside triphosphate) under which recA protein binds to single-stranded DNA without catalyzing D-loop formation and which are favorable for the DNase activities of the recBC enzyme. We found that the degradation of linear duplex DNA was unaffected, but that the endonuclease and exonuclease activities for single-stranded DNA were inhibited by about 50% and 35%, respectively. In contrast, no protection of circular duplex DNA containing single-stranded regions was observed. The results suggest that the recA protein by itself may not act as a potent inhibitor of recBC enzyme-dependent DNA degradation in vivo.