Recombination proteins and rescue of arrested replication forks.

Recombination proteins play crucial roles in the rescue of inactivated replication forks in Escherichia coli. The enzymes that catalyze the repair of DNA double-strand breaks by a classical strand-exchange reaction (RecBCD, RecA) act in two well-characterized fork repair pathways. They repair the DNA double-strand end made when a replication fork runs into a single-strand interruption. They reset the DNA double-strand end generated by replication fork reversal when a component of the replication machinery is inactivated. In addition, recombination proteins also act at replication forks in ways other than the classical strand-exchange reaction. For example, the RuvAB enzyme that catalyzes Holliday junction branch-migration during homologous recombination is also able to catalyze replication fork reversal in certain replication mutants, i.e. to convert certain blocked replication forks into Holliday junctions. Finally, some of the actions of recombination proteins after replication impairment are still unclear, as for example in UV-irradiated cells, where RecFOR and RecA catalyze gap repair but also participate, in a yet undefined way, in "replisome reactivation".