ATP-dependent DNA helicase that unwinds single- and double-stranded DNA in a 3'-5' direction (PubMed:9388193, PubMed:24816114, PubMed:25901030). Participates in DNA replication and repair (PubMed:12019152, PubMed:21325134, PubMed:23509288). Involved in 5'-end resection of DNA during double-strand break (DSB) repair: unwinds DNA and recruits DNA2 which mediates the cleavage of 5'-ssDNA (PubMed:21325134). Negatively regulates sister chromatid exchange (SCE) (PubMed:25901030). Stimulates DNA 4-way junction branch migration and DNA Holliday junction dissolution (PubMed:25901030). Binds single-stranded DNA (ssDNA), forked duplex DNA and DNA Holliday junction (PubMed:20639533, PubMed:24257077, PubMed:25901030). Recruited by the KHDC3L-OOEP scaffold to DNA replication forks where it is retained by TRIM25 ubiquitination, it thereby promotes the restart of stalled replication forks (By similarity). ATP + H2O = ADP + H(+) + phosphate Binds 1 zinc ion per subunit. Monomer (PubMed:28228481). Homodimer (via N-terminus) (PubMed:28228481). Homotetramer (via N-terminus); dimer of dimers (PubMed:28228481). Homohexamer (via N-terminus) (PubMed:28228481). Self-association negatively regulates DNA unwinding amplitude and rate. Oligomeric complexes dissociate into monomer in presence of ATP (PubMed:28228481). Part of the BRCA1-associated genome surveillance complex (BASC), which contains BRCA1, MSH2, MSH6, MLH1, ATM, BLM, PMS2 and the RAD50-MRE11-NBS1 protein complex. This association could be a dynamic process changing throughout the cell cycle and within subnuclear domains. Interacts with RMI complex. Interacts directly with RMI1 (via N-terminal region) component of RMI complex. Found in a complex, at least composed of BLM, RAD51 and SPIDR; the complex formation is mediated by SPIDR. Interacts with the KHDC3L/FILIA-OOEP/FLOPED scaffold complex and TRIM25 at DNA replication forks (By similarity). Interacts with ubiquitinated FANCD2 (PubMed:15257300). Interacts with SUPV3L1 (PubMed:17961633). Interacts with TOP3A (via N-terminal region). Interacts with SPIDR (via C-terminal region); the interaction is direct and required to target BLM to sites of DNA damage. Together with SPIDR, is redistributed in discrete nuclear DNA damage-induced foci following hydroxyurea (HU) or camptothecin (CPT) treatment. Accumulated at sites of DNA damage in a RMI complex- and SPIDR-dependent manner. The N-terminal region mediates dimerization and homooligomerization (PubMed:28228481). Both the helicase ATP-binding domain and the helicase C-terminal domain form intramolecular interactions with the HRDC domain in a ATP-dependent manner (PubMed:25901030). The HRDC domain is required for single-stranded DNA (ssDNA) and DNA Holliday junction binding (PubMed:20639533). Poly-ubiquitinated by TRIM25 at Lys-259. Phosphorylated in response to DNA damage. Phosphorylation requires the FANCA-FANCC-FANCE-FANCF-FANCG protein complex, as well as the presence of RMI1. The disease is caused by variants affecting the gene represented in this entry. Belongs to the helicase family. RecQ subfamily. BLM mutation db