Figure 4. Equilibrium binding affinities of APE1, apoAPE1 hOGG1, TDG, and hUNG to AP-DNA.

Binding data for TDG (black), hOGG1 (red), apoAPE1 (green), and hUNG (purple) for the AP site DNA (AP31^FAM; 10 nM) were obtained by fluorescence anisotropy measurements using buffer A at 20°C. Errors were estimated by performing three independent replicates of the titrations. In the case of hUNG, which showed very weak binding to the AP site, the saturating anisotropy value was fixed at a value previously observed in titrations using other salt concentrations where saturation could be achieved²⁰. This value was consistent with the extrapolated value predicted from the fit to the data set. The uncertainty in the weak K_D value for hUNG has no impact on any of our interpretations.