HEK 293T, Rad18−/− HCT116 (Shiomi et al., 2007 (link)), and U2OS cells were grown in high glucose DMEM (Gibco) with penicillin/streptomycin (Gibco), glutamine (Gibco), and 10% fetal bovine serum. Cells were damaged with MMS (Sigma-Aldrich), mitomycin C (Sigma-Aldrich), EMS (Sigma-Aldrich), 4-nitroquinoline 1-oxide (Sigma-Aldrich), aphidicolin (Sigma-Aldrich), camptothecin (Sigma-Aldrich), actinomycin D (EMD Millipore), etoposide (Sigma-Aldrich), hydrogen peroxide (Sigma-Aldrich), or cis-platinum (Sigma-Aldrich) at the indicated concentrations and times. Cells were also treated with ATR inhibitor (ATR-45; Charrier et al., 2011 (link)), ATM inhibitor (KU55933; Abcam), MG132 (Sigma-Aldrich), or LLnL (EMD Millipore) at the indicated concentrations and times.