Plays an essential role in the repair of DNA double-strand breaks by homologous recombination and in the repair of interstrand DNA cross-links (ICLs) by promoting FANCD2 monoubiquitination by FANCL and participating in recruitment to DNA repair sites. Required for maintenance of chromosomal stability. Specifically binds branched DNA: binds both single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). Participates in S phase and G2 phase checkpoint activation upon DNA damage. Interacts with FANCD2; the interaction is direct. Interacts with FANCL. Interacts with MTMR15/FAN1 (PubMed:17412408, PubMed:17460694, PubMed:20603015, PubMed:21775430). Interacts with POLN (PubMed:19995904). Observed in spots localized in pairs on the sister chromatids of mitotic chromosome arms and not centromeres, one on each chromatids. These foci coincide with common fragile sites. They are frequently interlinked through BLM-associated ultra-fine DNA bridges. The C-terminal 30 residues are probably required for function in DNA repair. Monoubiquitinated by FANCL on Lys-523 during S phase and upon genotoxic stress. Deubiquitinated by USP1 as cells enter G2/M, or once DNA repair is completed. Monoubiquitination requires the FANCA-FANCB-FANCC-FANCE-FANCF-FANCG-FANCM complex. Ubiquitination is required for binding to chromatin, DNA repair, and normal cell cycle progression. Monoubiquitination is stimulated by DNA-binding. Phosphorylated in response to DNA damage by ATM and/or ATR. The disease is caused by variants affecting the gene represented in this entry. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus.