Participates in DNA replication and repair. Exhibits a magnesium-dependent ATP-dependent DNA-helicase activity that unwinds single- and double-stranded DNA in a 3'-5' direction (By similarity). ATP-dependent DNA helicase that unwinds single- and double-stranded DNA in a 3'-5' direction. Participates in DNA replication and repair. Negatively regulates sister chromatid exchange (SCE). Stimulates DNA 4-way junction branch migration and DNA Holliday junction dissolution. Binds single-stranded DNA (ssDNA), forked duplex DNA and DNA Holliday junction. ATP + H2O = ADP + H(+) + phosphate Binds 1 zinc ion per subunit. Monomer. Homodimer (via N-terminus). Homotetramer (via N-terminus); dimer of dimers. Homohexamer (via N-terminus). Self-association negatively regulates DNA unwinding amplitude and rate. Oligomer forms dissociate into monomer in presence of ATP. The N-terminal region mediates dimerization and homooligomerization. Both the helicase ATP-binding domain and the helicase C-terminal domain form intramolecular interactions with the HRDC domain in a ATP-dependent manner. The HRDC domain is required for single-stranded DNA (ssDNA) and DNA Holliday junction binding. Belongs to the helicase family. RecQ subfamily.