Figure 4.

Template switching may provide the means to bypass or repair strand-specific DNA lesions. Fork regression (A,B) could allow the lagging strand to provide a template for extension of the blocked leading strand (B,C). Subsequent reversal of the original regression would result in bypass of the lesion and reinitiation of replication at the reconstituted fork structure (D). Note that such fork structures resemble the branched DNA found within D-loops and, at least in bacteria, replication reinitiation proteins can reload the replication apparatus back onto these forks. Alternatively, fork regression could reposition the lesion opposite an intact lagging strand template, promoting excision repair (B,E). Reversal of fork regression would again reform the fork to allow replication reinitiation (F).