PARP1 inhibition with olaparib or siRNA decreases ZNF-induced translocations. (A) HEK 293T cells were treated with olaparib and transfected with siRNA and ZFNs at the times indicated in the schematic above. Olaparib and siRNA knockdown of PARP1 repressed ZFN-induced translocations, as assayed by semiquantitative PCR of the der[3] product. Data are representative of 3 independent determinations. Translocations are induced by two ZFN pairs that create 2 simultaneous DSBs in target chromosomes, but not by the negative control single ZFNs of each pair. (B) Quantification of ZFN-induced translocations with or without olaparib; values are averages (± SEM) for 3 determinations. (C) Quantification of ZFN-induced translocations with or without siRNA repression of PARP1; values are averages (± SEM) for 3 determinations, with SEM too small for bars to be visible.