Cell Line Propagation and Validation

HEK293A, HeLa, and OVCAR3 cells were purchased from the American Type Culture Collection (ATCC); HEK293A and HeLa cells were cultured in DMEM with 10% fetal bovine serum, while OVCAR3 cells were cultured in RPMI with 10% fetal bovine serum. RPE1-hTERT FLAG-Cas9 TP53−/− BRCA1−/− cells were a gift that was kindly provided by Dr. Daniel Durocher (University of Toronto) and were cultured in DMEM with 10% fetal bovine serum. RMUGS was obtained from the Japanese Collection of Research Bioresources Cell Bank and cultured in Ham’s F12 medium with 10% fetal bovine serum. Knockout cells generated in 293 A and HeLa cells were created with pLentiCRISPRv2 (Addgene, #52961) containing indicated gRNAs (Figure 7—figure supplement 1), as described previously (Wang et al., 2021 (link)). All knockout cells were validated by western blotting and DNA sequencing (Figure 7—figure supplement 1). The 293A-derived PARP1/2 DKO cells were the same as those in the previous study (Wang et al., 2021 (link)). All cell lines were free of mycoplasma contamination.