ATP-dependent DNA helicase that unwinds double-stranded (ds)DNA in a 3'-5' direction (PubMed:24816114, PubMed:25901030, PubMed:9388193, PubMed:9765292). Participates in DNA replication and repair (PubMed:12019152, PubMed:21325134, PubMed:23509288, PubMed:34606619). 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). Stimulates DNA 4-way junction branch migration and DNA Holliday junction dissolution (PubMed:25901030). Binds single-stranded DNA (ssDNA), forked duplex DNA and Holliday junction DNA (PubMed:20639533, PubMed:24257077, PubMed:25901030). Unwinds G-quadruplex DNA; unwinding occurs in the 3'- 5' direction and requires a 3' single-stranded end of at least 7 nucleotides (PubMed:18426915, PubMed:9765292). Helicase activity is higher on G-quadruplex substrates than on duplex DNA substrates (PubMed:9765292). Telomeres, immunoglobulin heavy chain switch regions and rDNA are notably G-rich; formation of G-quadruplex DNA would block DNA replication and transcription (PubMed:18426915, PubMed:9765292). Negatively regulates sister chromatid exchange (SCE) (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). {ECO:0000250|UniProtKB:O88700, ECO:0000269|PubMed:12019152, ECO:0000269|PubMed:18426915, ECO:0000269|PubMed:20639533, ECO:0000269|PubMed:21325134, ECO:0000269|PubMed:23509288, ECO:0000269|PubMed:24257077, ECO:0000269|PubMed:24816114, ECO:0000269|PubMed:25901030, ECO:0000269|PubMed:34606619, ECO:0000269|PubMed:9388193, ECO:0000269|PubMed:9765292}. (Microbial infection) Eliminates nuclear HIV-1 cDNA, thereby suppressing immune sensing and proviral hyper-integration. . This is the function of Ensembl gene identifier ENSG00000197299 (BLM, BLM RecQ like helicase).