A dynamic RecA filament permits DNA polymerase-catalyzed extension of the invading strand in recombination intermediates.

Recombination-dependent replication is an essential housekeeping function in prokaryotes and eukaryotes, serving, for example, to restart DNA replication after the repair of a double-strand break. Little is known about the interplay between the recombination and replication machinery when recombination intermediates are used as substrates for DNA replication. We show here that recombination intermediates formed between linear duplex and supercoiled plasmid DNAs are substrates for a generalized strand displacement DNA synthesis reaction in which the 3'-OH of the invading strand in the recombination intermediate is used as a primer. DNA synthesis is driven by negative superhelicity and is inhibited if disassembly of the RecA filament is prevented. Thus, assembly and disassembly of RecA filaments in the same direction facilitates filament clearance from the 3'-end of the invading strand, allowing DNA synthesis to occur from recombination intermediates.