Plays a critical role in recombination and DNA repair. Helps process Holliday junction (HJ) intermediates to mature products by catalyzing branch migration. Has replication fork regression activity, unwinds stalled or blocked replication forks to make a HJ that can be resolved by RuvC or RusA. Also rewinds unwound dsDNA in an ATP-dependent manner. Has double-stranded (ds)DNA unwinding activity characteristic of a DNA helicase with 3'-5' polarity in vitro on linear dsDNA; branched duplex DNA (Y-DNA) substrates adopt different conformations that influence which of the two arms are unwound. Binds and unwinds HJ and Y-DNA but not linear duplex DNA; binds no more than 10 nucleotides of ssDNA at a fork. Has a role in constitutive stable DNA replication (cSDR, DNA replication in the absence of protein synthesis) and R-loop (RNA annealed with dsDNA) formation. Unwinds R-loops but not RNA:DNA hybrids. Is genetically synergistic to RadA and RuvABC