Fig. 8

Mechanisms for DSB repair in eukaryotes. The structures down the center of the figure are as proposed by Szostak, with resolution of the double Holliday junction to give either crossover or non-crossover products (see Fig. 4b). Additional repair pathways are (1) nonhomologous end joining (NHEJ) in eukaryotes and some bacteria and (2) synthesis-dependent strand annealing (SDSA). The invading DNA strand is extended by DNA polymerase but the heteroduplex DNA is unwound and re-pairs with the original duplex. Further synthesis and ligation gives only non-crossover products. (3) The double Holliday junctions are dissolved (“dissolution”) by the combined action of a DNA helicase and topoisomerase to give only non-crossover products (After Jasin and Rothstein 2013)