Required for maintenance of chromosomal stability. Promotes accurate and efficient pairing of homologs during meiosis. Involved in the repair of DNA double-strand breaks, both by homologous recombination and single-strand annealing. May participate in S phase and G2 phase checkpoint activation upon DNA damage. Plays a role in preventing breakage and loss of missegregating chromatin at the end of cell division, particularly after replication stress. Required for the targeting, or stabilization, of BLM to non-centromeric abnormal structures induced by replicative stress. Promotes BRCA2/FANCD1 loading onto damaged chromatin. May also be involved in B-cell immunoglobulin isotype switching. Interacts directly with FANCE and FANCI. Interacts with USP1 and MEN1. The ubiquitinated form specifically interacts with BRCA1 and BLM. Both the nonubiquitinated and the monoubiquitinated forms interact with BRCA2; this interaction is mediated by phosphorylated FANCG and the complex also includes XCCR3. The ubiquitinated form specifically interacts with MTMR15/FAN1 (via UBZ-type zinc finger), leading to recruit MTMR15/FAN1 to sites of DNA damage. Interacts with DCLRE1B/Apollo. Highly expressed in germinal center cells of the spleen, tonsil, and reactive lymph nodes, and in the proliferating basal layer of squamous epithelium of tonsil, esophagus, oropharynx, larynx and cervix. Expressed in cytotrophoblastic cells of the placenta and exocrine cells of the pancreas. Highly expressed in testis, where expression is restricted to maturing spermatocytes. 4 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.