Different binding kinetics of XRCC1 and PCNA at DNA repair sites. FLIP data from 9 individual experiments are shown as mean curves. The scheme of the experiment is outlined in the inset. Two separate subnuclear spots of transiently transfected Hela cells were microirradiated. Half of the nucleus containing one irradiated site was repeatedly bleached for 1 s over a total time period of 150 s, starting 5 min after microirradiation. The decay of the fluorescence intensity at the microirradiated site within the non-bleached half of the nucleus was measured and plotted over time. Error bars represent the standard error of the mean.