DNA-dependent ATPase and 5'-3' DNA helicase required for the maintenance of chromosomal stability. Acts late in the Fanconi anemia pathway, after FANCD2 ubiquitination. Involved in the repair of DNA double-strand breaks by homologous recombination in a manner that depends on its association with BRCA1. Involved in the repair of abasic sites at replication forks by promoting the degradation of DNA-protein cross-links: acts by catalyzing unfolding of HMCES DNA-protein cross-link via its helicase activity, exposing the underlying DNA and enabling cleavage of the DNA-protein adduct by the SPRTN metalloprotease. Can unwind RNA:DNA substrates. Unwinds G-quadruplex DNA; unwinding requires a 5'-single stranded tail