Single-stranded 3'-5' DNA helicase that plays a key role in homology-driven double-strand break (DSB) repair (PubMed:24005329, PubMed:24005041). 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) (By similarity). Possesses both DNA unwinding and annealing activities (By similarity). Forms a complex with RAD51, stimulating HELQ DNA helicase activity and ability to unwing DNA (By similarity). Efficiently unwinds substrates containing 3' overhangs or a D-loop (By similarity). In contrast, interaction with the replication protein A (RPA/RP-A) complex inhibits DNA unwinding by HELQ but strongly stimulates DNA strand annealing (By similarity). Triggers displacement of RPA from single-stranded DNA to facilitate annealing of complementary sequences (By similarity). ATP + H2O = ADP + H(+) + phosphate Hexamer (By similarity). Interacts with POLN (By similarity). Interacts with RAD51B (By similarity). Interacts with RAD51C; promoting association with the BCDX2 complex (PubMed:24005329). Interacts with the replication protein A (RPA/RP-A) complex (By similarity). Interacts with RAD51; stimulating HELQ DNA helicase activity and ability to unwing DNA (By similarity). Localizes to sites of DNA damage; localizes to damaged replication forks. Mice display Fanconi anemia-like phenotypes, characterized by subfertility, germ cell attrition, interstrand cross-links (ICLs) sensitivity and cancer susceptibility. Belongs to the helicase family. SKI2 subfamily.