The Escherichia coli replisome is inherently DNA damage tolerant.

The Escherichia coli DNA replication machinery must frequently overcome template lesions under normal growth conditions. Yet, the outcome of a collision between the replisome and a leading-strand template lesion remains poorly understood. Here, we demonstrate that a single, site-specific, cyclobutane pyrimidine dimer leading-strand template lesion provides only a transient block to fork progression in vitro. The replisome remains stably associated with the fork after collision with the lesion. Leading-strand synthesis is then reinitiated downstream of the damage in a reaction that is dependent on the primase, DnaG, but independent of any of the known replication-restart proteins. These observations reveal that the replisome can tolerate leading-strand template lesions without dissociating by synthesizing the leading strand discontinuously.