Updated project metadata. We used homologous recombination based CRISPR Knock-in strategy to insert a SFB tag at C terminal of 53BP1 in 293T cells. We performed tandem affinity purification of endogenous 53BP1 in both soluble and chromatin fraction to uncover known and new 53BP1 binding proteins which might play roles in DNA damage response. We identified and examined FOXK1 for its role in DNA damage response through the interaction with 53BP1 mainly in soluble fraction.