Figure 1

DSBs can be repaired by several HR repair pathways including DSBR (double-strand break repair) and SDSA (synthesis-dependent strand annealing). HR is initiated by resection of a DSB to provide 3’ ssDNA overhangs. Strand invasion by these 3’ ssDNA overhangs into a homologous sequence is followed by DNA synthesis at the invading end. After strand invasion and synthesis, the second DSB end can be captured to form an intermediate with two HJs. After gap-repair DNA synthesis and ligation, the structure is resolved at the HJs in a non-crossover (red arrow heads at both HJs) or crossover mode (orange arrow heads at one HJ and red arrow heads at the other HJ). Alternatively, the reaction can proceed to SDSA by strand displacement, annealing of the extended single-strand end to the ssDNA on the other break end, followed by gap-filling DNA synthesis and ligation. The repair product from SDSA is always non-crossover.