Single-stranded 3'-5' DNA helicase that plays a key role in homology-driven double-strand break (DSB) repair (PubMed:11751861, PubMed:19995904, PubMed:21398521, PubMed:24005041, PubMed:24005565, PubMed:34316696, PubMed:34937945). Involved in different DSB repair mechanisms that are guided by annealing of extensive stretches of complementary bases at break ends, such as microhomology-mediated end-joining (MMEJ), single-strand annealing (SSA) or synthesis-dependent strand annealing (SDSA) (PubMed:34937945). Possesses both DNA unwinding and annealing activities (PubMed:34937945). Forms a complex with RAD51, stimulating HELQ DNA helicase activity and ability to unwing DNA (PubMed:34937945). Efficiently unwinds substrates containing 3' overhangs or a D-loop (PubMed:21398521, PubMed:34937945). In contrast, interaction with the replication protein A (RPA/RP-A) complex inhibits DNA unwinding by HELQ but strongly stimulates DNA strand annealing (PubMed:34937945). Triggers displacement of RPA from single-stranded DNA to facilitate annealing of complementary sequences (PubMed:34316696, PubMed:34937945). ATP + H2O = ADP + H(+) + phosphate ATPase activity is strongly stimulated by single-stranded DNA (PubMed:11751861). Presence of ATP and Mg cofactor are required for helicase activity allowing to unwind duplex oligonucleotides up to 60-70-mer (PubMed:11751861). This helicase activity is stimulated by replication protein A (RPA/RP-A) complex that binds to unwound regions and inhibits re-annealing (PubMed:11751861). Homodimer (PubMed:34316696). Interacts with POLN (PubMed:19995904). Interacts with RAD51B and RAD51C; promoting association with the BCDX2 complex (PubMed:24005041). Interacts with the replication protein A (RPA/RP-A) complex (PubMed:34316696, PubMed:34937945). Interacts with RAD51; stimulating HELQ DNA helicase activity and ability to unwing DNA (PubMed:34937945). Localizes to sites of DNA damage; localizes to damaged replication forks. Belongs to the helicase family. SKI2 subfamily.