recA protein binding to the heteroduplex product of DNA strand exchange.

Following DNA strand exchange, recA protein remains associated with the heteroduplex DNA product of the reaction. This association exists without significant changes (as measured by nuclease protection, topological state of the heteroduplex DNA, and rates of ATP hydrolysis) for at least 30 min after strand exchange is complete. The heteroduplex DNA is unwound as a result of this association to an extent at least as great as the unwinding observed when recA protein is bound to duplex DNA at pH 6.35. The extensive unwinding, in combination with the rates of ATP hydrolysis reported elsewhere, provide evidence that recA protein binding is contiguous throughout the heteroduplex DNA. This binding is disrupted upon challenge with heterologous single-stranded DNA, with rapid migration of recA protein to the challenging DNA. These results are discussed in relation to the mechanism of recA protein-promoted branch migration.