Single-stranded 3'-5' DNA helicase that plays a key role in homology-driven double-strand break (DSB) repair (PubMed:16888338). 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). ATP + H2O = ADP + H(+) + phosphate Localizes to sites of DNA damage. Impaired meiosis, leading to maternal mutants with eggshell defects (PubMed:9362456, PubMed:16888338). Mutant females produce ventralized egg shells, with phenotypes ranging from fused dorsal appendages to fully ventralized eggs with no dorsal appendages (PubMed:16888338). Mutant flies are hypersensitive to chemical mutagens (PubMed:16888338). Belongs to the helicase family. SKI2 subfamily.