BCR/ABL promotes unfaithful repair of DSBs. Parental and BCR/ABL-Draa-40 cells were transfected with I-SceI expression plasmid to induce a DSB in the reporter DR-GFP cassette. (A) The scheme illustrates the consequences of I-SceI-induced DSB in DR-GFP. HRR restores BcgI restriction site (left branch), and NHEJ results in the loss of both I-SceI and BcgI sites (right branch). Repair products were amplified 72 hours later by PCR using primers A and B, cloned, and expressed in the competent bacteria. HRR (BcgI-positive) and NHEJ (BcgI-negative/I-SceI-negative) products were identified by Southern analysis (200 bacterial clones/group analyzed), amplified by PCR using primers C and D, or T3 and T7, respectively, and sequenced (20 sequences/group analyzed) to determine the repair mechanism (percentage of reparation events) and its fidelity (mutation frequency for HRR, and gain/loss of DNA base pairs for NHEJ). The mutation phenotype in the 725-bp HRR products in BCR/ABL cells is shown in the bottom left diagram; gain/loss of DNA in the individual NHEJ products in parental and BCR/ABL cells is shown in the bottom right diagram. (B) Individual mutations in the HRR products in BCR/ABL cells are shown (red numbers indicate the number of mutations detected at the particular base). BcgI restriction site sequence is boxed.