Multifunctional protein that is involved in the regulation of many processes including cell proliferation, apoptosis, cell cycle progression or transcription (PubMed:18039846, PubMed:20015864). Regulates the proliferation of neuronal stem cells, differentiation of leukemic cells and progression from G1 to S phase of the cell cycle. As negative regulator of caspase-3-dependent apoptosis, may act as an antagonist of ANP32A in regulating tissue homeostasis (PubMed:20015864). Exhibits histone chaperone properties, able to recruit histones to certain promoters, thus regulating the transcription of specific genes (PubMed:18039846, PubMed:20538007). Also plays an essential role in the nucleocytoplasmic transport of specific mRNAs via the uncommon nuclear mRNA export receptor XPO1/CRM1 (PubMed:17178712). Participates in the regulation of adequate adaptive immune responses by acting on mRNA expression and cell proliferation (By similarity). {ECO:0000250|UniProtKB:Q9EST5, ECO:0000269|PubMed:17178712, ECO:0000269|PubMed:18039846, ECO:0000269|PubMed:20015864, ECO:0000269|PubMed:20538007}. (Microbial infection) Plays an essential role in influenza A and B viral genome replication (PubMed:31217244, PubMed:33045004). Also plays a role in foamy virus mRNA export from the nucleus to the cytoplasm (PubMed:21159877). {ECO:0000269|PubMed:21159877, ECO:0000269|PubMed:31217244, ECO:0000269|PubMed:33045004}. This is the function of ENSG00000136938 (ANP32B, acidic nuclear phosphoprotein 32 family member B).