Figure 1.
Second-end capture in DSB repair based on the migrating D-loop version (Ferguson and Holloman, 1996) of synthesis dependent strand annealing. DSB is resected to reveal a protruding 3′-single-strand tail, which invades a homologous duplex to form a D-loop. With DNA synthesis to extend the invading strand the D-loop migrates until there is overlap in sequence with the second end of the DSB. If the D-loop collapses releases invading strand it can anneal with complementary strand on the second end of the DSB to reunite the broken ends. Alternatively the displaced strand of the d-loop can pair with the second end. The D-loop annealed with complementary single strand is magnified to show in isolation the duplexed D-loop structure. With additional DNA synthesis and ligation a Holliday junction-containing intermediate forms. Resolution can result in crossover or non-crossover outcomes.