Pre-incubation of RFC with ATP, PCNA enables ptDNA-dependent rapid ATP hydrolysis. (A) Single-mixing stopped-flow experiments measuring pre-steady state Pi release kinetics show that ptDNA is required for rapid ATP hydrolysis and Pi release by RFC; highest activity is detected with PCNA plus ptDNA (blue trace).(B) Sequential-mixing stopped-flow experiments show that pre-incubation of RFC with ATP (Δt = 3 s shown) enables ptDNA to trigger a burst of ATP hydrolysis and Pi release (purple trace). The burst kinetics are maximal when PCNA is included during pre-incubation (orange and green traces versus blue trace). Final reagent concentrations: 0.5 μM RFC, 500 μM ATP, 2.5 μM PCNA, 2.5 μM ptDNA, 10 μM MDCC-PBP.