XRCC1 and cancer: For nick DNA-binding affinity of XRCC1 wild-type (Fig. 3B) and the cancer-associated variants (Fig. S8) to the repair intermediate with correctly base-paired 3′-dG:C ends, we observed similar KD values that were in the range of ∼50 to 60 nM with XRCC1 variants R194W and R399Q, while P161L and Y576S (KD: ∼90–110 nM) show a relatively lower affinity constant.