DNA helicase that plays an important role in DNA replication, transcription and repair. Binds to the RNA polymerase II subunit POLR2A during transcription elongation and suppresses transcription-associated genomic instability. Associates also with POLR1A and enforces the stability of ribosomal DNA arrays. Plays an important role in mitotic chromosome separation after cross-over events and cell cycle progress. Mechanistically, removes RAD51 filaments protecting stalled replication forks at common fragile sites and stimulates MUS81-EME1 endonuclease leading to mitotic DNA synthesis. Required for efficient DNA repair, including repair of inter-strand cross-links. Stimulates DNA decatenation mediated by TOP2A. Prevents sister chromatid exchange and homologous recombination. ATP + H2O = ADP + H(+) + phosphate Monomer. Interacts with TOP2A, TOP3A and TOP3B. Interacts with RNA polymerase II subunit POLR2A. Identified in a complex with the RNA polymerase II core bound to DNA. Interacts with RAD51 (By similarity). Interacts with WRN; this interaction stimulates WRN helicase activity on DNA fork duplexes (By similarity). Interacts with MUS1; this interaction promotes MUS81-dependent mitotic DNA synthesis (By similarity). Recruited to sites of DNA damage, such as single-strand breaks and inter-strand cross-links, and at stalled replication forks. Phosphorylated by CDK1 at Ser-728; this phosphorylation is required for RECQL5-mediated disruption of RAD51 filaments on stalled replication forks. Belongs to the helicase family. RecQ subfamily.