A, Cyclin E overexpression results in increased RMD when the DSB is close to one repeat. The U2OS (EGFP-SSA-3427-3) cell line carrying Tet-on-cyclin E plasmid was used, and RMD frequency was determined with or without induction of cyclin E expression by doxycycline (DOX, 0.5 µg/mL), which was added 24 hours before transfection of the indicated sgRNAs/Cas9. Cyclin E expression levels were validated by Western blot, using KU70 as the loading control. 