End joining of BstXI substrates by PCO cultures. End joining of BstXI substrates by PCO cultures. A, Quantification of PCO rejoining of Co substrates. Results are representative of three independent experiments. OSEC2 and V3YAC (DNA-PKcs corrected) were used as positive controls. V3 (DNA-PKcs deficient) cell line was used as a negative control. Water was used as a contamination control. Error bars are SEM. PCO, N = 47. B, Representative image of GelRed detection of end joining of BstXI compatible substrates by PCO cultures. C, Representative image of PCR analysis of rejoined DNA of Co and 2I substrates amplified using pFOR and pREV primers. Correct rejoining produces products of 551 bp. Inaccurate rejoining with loss of bases results in smaller or no product formation. Aiste McCormick et al. Clin Cancer Res 2017;23:2050-2060 ©2017 by American Association for Cancer Research