Non-specific DNA-binding protein that plays key roles in mitotic nuclear reassembly, chromatin organization, DNA damage response, gene expression and intrinsic immunity against foreign DNA (PubMed:10908652, PubMed:11792822, PubMed:12163470, PubMed:18005698, PubMed:25991860, PubMed:28841419, PubMed:32792394). Contains two non-specific double-stranded DNA (dsDNA)-binding sites which promote DNA cross-bridging (PubMed:9465049). Plays a key role in nuclear membrane reformation at the end of mitosis by driving formation of a single nucleus in a spindle-independent manner (PubMed:28841419). Transiently cross-bridges anaphase chromosomes via its ability to bridge distant DNA sites, leading to the formation of a dense chromatin network at the chromosome ensemble surface that limits membranes to the surface (PubMed:28841419). Also acts as a negative regulator of innate immune activation by restricting CGAS activity toward self-DNA upon acute loss of nuclear membrane integrity (PubMed:32792394). Outcompetes CGAS for DNA-binding, thereby preventing CGAS activation and subsequent damaging autoinflammatory responses (PubMed:32792394). Involved in the recognition of exogenous dsDNA in the cytosol: associates with exogenous dsDNA immediately after its appearance in the cytosol at endosome breakdown and is required to avoid autophagy (PubMed:25991860). In case of poxvirus infection, has an antiviral activity by blocking viral DNA replication (PubMed:18005698). (Microbial infection) Exploited by retroviruses for inhibiting self-destructing autointegration of retroviral DNA, thereby promoting integration of viral DNA into the host chromosome (PubMed:9465049, PubMed:11005805, PubMed:16680152). EMD and BAF are cooperative cofactors of HIV-1 infection (PubMed:16680152). Association of EMD with the viral DNA requires the presence of BAF and viral integrase (PubMed:16680152). The association of viral DNA with chromatin requires the presence of BAF and EMD (PubMed:16680152). Homodimer (PubMed:16337940, PubMed:22399800, PubMed:28841419). Heterodimerizes with BANF2 (PubMed:16337940). Interacts with ANKLE2/LEM4, leading to decreased phosphorylation by VRK1 and promoting dephosphorylation by protein phosphatase 2A (PP2A) (PubMed:22770216). Binds non-specifically to double-stranded DNA, and is found as a hexamer or dodecamer upon DNA binding. Binds to LEM domain-containing nuclear proteins such as LEMD3/MAN1, TMPO/LAP2 and EMD (emerin) (PubMed:11792822, PubMed:15681850). Interacts with ANKLE1 (via LEM domain); the interaction may favor BANF1 dimerization (PubMed:22399800). Interacts with CRX and LMNA (lamin-A). Binds linker histone H1.1 and core histones H3 (PubMed:16203725). Interacts with LEMD2 (via LEM domain) (PubMed:32494070). (Microbial infection) Interacts with HIV-1 pre-integration complex in cytoplasm by binding to viral matrix protein and Gag polyprotein. Significantly enriched at the nuclear inner membrane, diffusely throughout the nucleus during interphase and concentrated at the chromosomes during the M-phase (PubMed:16495336, PubMed:24600006). The phosphorylated form (by VRK1) shows a cytoplasmic localization whereas the unphosphorylated form locates almost exclusively in the nucleus (PubMed:16495336, PubMed:24600006). May be included in HIV-1 virions via its interaction with viral GAG polyprotein (PubMed:14645565). Widely expressed. Expressed in colon, brain, heart, kidney, liver, lung, ovary, pancreas, placenta, prostate, skeletal muscle, small intestine, spleen and testis. Not detected in thymus and peripheral blood leukocytes. Has a helix-hairpin-helix (HhH) structural motif conserved among proteins that bind non-specifically to DNA. LEM domain proteins bind centrally on the BAF dimer. Ser-4 is the major site of phosphorylation as compared to Thr-2 and Thr-3. Phosphorylation on Thr-2; Thr-3 and Ser-4 disrupts its ability to bind DNA and reduces its ability to bind LEM domain-containing proteins. Non phosphorylated BAF seems to enhance binding between EMD and LMNA. Dephosphorylated by protein phosphatase 2A (PP2A) following interaction with ANKLE2/LEM4 during mitotic exit, leading to mitotic nuclear envelope reassembly. (Microbial infection) Phosphorylated by poxvirus B1 kinase (VPK1) on serine and threonine residues, leading to BANF1 relocalization to the cytoplasm, loss of dimerization and impaired DNA binding activity. (Microbial infection) Phosphorylated at the N-terminus by vaccinia virus (VacV) B1 kinase, leading to BANF1 relocalization to the cytoplasm, loss of dimerization and impaired DNA binding activity (PubMed:24600006, PubMed:16495336). Hyperphosphorylation is linked to the loss of ability to suppress vaccinia virus replication (PubMed:24600006). The disease is caused by variants affecting the gene represented in this entry. Belongs to the BAF family.