Fig. 3.

TOP2 poison induces translocation mediated by the DSB repair pathway. TOP2 poison-mediated DSB is likely to be repaired by two pathways, NHEJ or HR repair. NHEJ can repair precisely when the DSB at a low concentration level. If DSB accumulates to a high concentration level, it may cause sequence deletion and translocation. NHEJ mainly contains three types of repair products, faithful repair, sequence loss, and translocation. HR is mediated by a homologous sequence. According to the model sequence, it may produce a different product. In most cases, HR repair uses homologous sequences as templates. This situation generates mainly a crossover or a non-crossover product through two pathways, including SDSA and DSBR, which play an instrumental role in meiosis. In a few cases, precision repair occurs when HR repair uses the same sequence as a template, and translocations may happen when HR uses a non-homologous sequence as a template. The blue and the red chromosomes are homologous, while the orange indicates a non-homologous chromosome. The blue arrowheads are located at one of the Holliday junctions (HJ), and the red arrowheads are located at the other junctions.