Investigation of t(15;17) translocation mechanism in UPN 14 by in vitro topoisomerase IIα DNA cleavage assay. DNA cleavage assays are shown for PML (A) and RARA (B) genomic breakpoint regions. For the PML assay, the reverse complement of the substrate containing the “hotspot” region between 1482 and 1489 described by Mistry et al⁵  was used. Lanes 1 to 9 of each cleavage assay are described in the legend to Figure 2. (C) Native PML and RARA sequences are shown in red and blue, respectively. In the creation of PML-RARA, processing includes exonucleolytic deletion and repair via the NHEJ pathway. In the creation of RARA-PML, 2-base homologies facilitate repair via the NHEJ pathway, whereas in both instances polymerization of the relevant overhangs fills in any remaining gaps (shown in black font).