B, RMD assays performed after DSBs have been generated by sgRNAs/Cas9. The distance between the sgRNA/Cas9 cleavage sites and the repeat sequences is indicated. U2OS cells carrying a single copy of the EGFP-SSA reporter (3427-17) were transfected with sgRNA/Cas9 plasmids, and the percentage of GFP-positive cells was determined (left). U2OS cells transfected with the indicated reporters EGFP-SSA-17/6 bp, EGFP-SSA-0.3 kb, EGFP-SSA-0.6 kb and EGFP-SSA-1.0 kb were pooled as a population after selection of the drug marker on the reporters, followed by sgRNA/Cas9 cleavage (right). 