Inhibition of ROS production increased end-joining efficiency and fidelity. Nuclear extracts of cells treated with CEP-701 show increased end-joining efficiency and fidelity. (A) MOLM-14 nuclear extracts were used in in vitro end-joining assay using a plasmid cut with restriction enzyme SmaI. The photomicrograph shows increased repair efficiency (lanes 4,5) and fidelity (lanes 9,10) in FLT3-inhibited extracts. Left side of the gel shows efficiency, and on the right side end-joined products were recut with restriction enzyme, SmaI, used for initial cutting. Experiments were performed in duplicate. Lanes 1 and 6: negative controls; lanes 2 and 7: ligation was performed with T4 ligase; lanes 3 and 8: ligation was performed with nuclear extracts from untreated cells; lanes 4 and 9: ligation was performed with nuclear extracts from cells treated with 50 nM CEP-701; and lanes 5 and 10: ligation was performed with nuclear extracts from cells treated with 100 nM CEP-701. (B) Graphic representation of the end-joining experiment in panel A. More end-joined products were observed in CEP-701–treated samples than untreated ones. In addition, an increased amount of correctly end-joined products were observed in CEP-701–treated samples. (C,D) Similar experiments as performed for panels A,B were performed with MV-4-11 cells. The black bars represent efficiency of repair, and the gray bars represents fidelity of repair (ie, percentage of product cut by the restriction enzyme). The error bars represent plus or minus SEM.