Effect of RecO on RecA nucleation and polymerization. Circular pGEM3 Zf (+) ssDNA (10 μM in nt) was pre-incubated with the indicated concentration of RecO for 5 min at 37°C in buffer A containing 5 mM ATP or dATP. Then RecA (0.8 μM) was added and the (d)ATPase activity measured for 25 min. All reactions were repeated three or more times with similar results. The amount of ATP or dATP hydrolyzed was calculated as described in 'Materials and Methods' section.