Twenty million cells were harvested for chromatin immunoprecipitation (ChIP) using an anti-RAD51 (10ug/sample) or anti-RPA antibody (10ug/sample). ssDNA that spontaneously forms hairpins after heat renaturation was then enriched and sequenced as described (Brick et al., 2018) Libraries were quantified using with the KAPA Library Quantification Kit (Kapa Biosciences) and sequenced in a NextSeq 550 system (Illumina, 75 bp single end reads). libraries were prepared and sequenced following standard Illumina protocols