UvrD helicase, unlike Rep helicase, dismantles RecA nucleoprotein filaments in Escherichia coli

The roles of UvrD and Rep DNA helicases of Escherichia coli are not yet fully understood. In particular, the reason for rep uvrD double mutant lethality remains obscure. We reported earlier that mutations in recF, recO or recR genes suppress the lethality of uvrD rep, and proposed that an essential activity common to UvrD and Rep is either to participate in the removal of toxic recombination intermediates or to favour the proper progression of replication. Here, we show that UvrD, but not Rep, directly prevents homologous recombination in vivo. In addition to RecFOR, we provide evidence that RecA contributes to toxicity in the rep uvrD mutant. In vitro, UvrD dismantles the RecA nucleoprotein filament, while Rep has only a marginal activity. We conclude that UvrD and Rep do not share a common activity that is essential in vivo: while Rep appears to act at the replication stage, UvrD plays a role of RecA nucleoprotein filament remover. This activity of UvrD is similar to that of the yeast Srs2 helicase.