The complex of DNA ligase 3 (LIG3) and XRCC1 is necessary for the completion of microhomology-mediated end joining (MMEJ), although DNA ligase 1 (LIG1) may also be involved (Sharma et al. 2015). LIG3:XRCC1 is recruited to MMEJ sites by the MRN complex and ligates single strand nicks that remain after reparative DNA synthesis by DNA polymerase theta (POLQ) at DNA double strand break (DSB) sites (Della-Maria et al. 2011). The annealing of microhomology regions between two 3'-ssDNA overhangs of resected DNA DSBs during MMEJ leads to deletion of the intervening DNA sequence and one of the microhomology regions in repaired double strand DNA (dsDNA) (Ghezraoui et al. 2014). In addition, as POLQ is error-prone, repaired DNA contains base substitutions (Ceccaldi et al. 2015). Similar to nonhomologous end joining (NHEJ), MMEJ (also known as alternative-NHEJ) can also produce translocations by joining unrelated DNA molecules (Ghezraoui et al. 2014).