DNA-dependent ATPase and 3'-5' DNA helicase that may be involved in repair of stalled replication forks. A low processivity 3'-5' helicase. Unwinds short dsDNA substrates with 3'-overhangs (25 bp dsDNA with 25 base overhang), less active on longer dsDNA substrates. Also unwinds the lagging strand of a stalled replication fork (but the leading strand was not tested). Binds ssDNA, but dsDNA about 35-fold less well. Able to displace streptavidin from biotinylated ssDNA, which is partially inhibited by DNA-binding proteins, suggesting it may play a role in stripping proteins from stalled replication forks. ATP + H2O = ADP + H(+) + phosphate Monomer. Crystallizes with 5 domains; the first 4 form a ring through which ssDNA may pass (seen in A. fulgidus crystals). The C-terminal domain (654-715) lies perpendicular to the ring and is able to bind ssDNA, which may cause it to may act as a molecular brake, inhibiting helicase activity (PubMed:18056710). Belongs to the helicase family. Hel308 subfamily.