Updated publication reference for PubMed record(s): 30445466. RNF8 is a key E3 ubiquitin ligase functioning in both DSB- and UV-induced DDR, identification of additional substrates will help further elucidate its role in DNA damage signaling. To identify substrates of ubiquitin ligases, we have recently devised a method based on proximity-dependent biotin labeling. In this method, an E3 ubiquitin ligase of interest is expressed as a fusion to Escherichia coli biotin ligase BirA together with a biotin acceptor peptide (AP)-tagged ubiquitin. The BirA-directed biotin labeling of AP depends on the proximity of the two fusion proteins in the cell, which leads to preferential labeling of ubiquitinated E3 substrates. In this study, we applied this procedure to RNF8 and identified its substrates.