Fig. 3.

Model for recombination initiated by breakage and strand invasion. (A) Template strand breakage occurs 5′ to one or the other of the T-T (6-4) photoadducts when replication forks have stalled. (B) Strand invasion promotes annealing of nascent strands, which allows each of them to be extended and, after the reannealing of the nascent strands to their original templates, the completion of plasmid replication. Some limited extension of the invading template 3′ end can also occur, requiring resection of one or the other broken ends to reconstruct the broken strand. Full plasmid replication results in strands as depicted in Fig. 2C. Solid lines, original template strands; dotted lines, strand segments replicated before stalling at the photoadduct sites; dashed lines, strand segments replicated after strand invasion and the annealing of nascent strands.