Multifunctional protein that is involved in the regulation of many processes including cell proliferation, apoptosis, cell cycle progression or transcription (PubMed:20015864, PubMed:18039846). 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:20538007, PubMed:18039846). 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). (Microbial infection) Plays an essential role in influenza A and B viral genome replication (PubMed:33045004, PubMed:31217244). Also plays a role in foamy virus mRNA export from the nucleus to the cytoplasm (PubMed:21159877). Interacts with histones H3 and H4 (PubMed:20538007). Interacts with KLF5; this interaction induces promoter region-specific histone incorporation and inhibition of histone acetylation by ANP32B (PubMed:18039846). (Microbial infection) Interacts with Sendai virus protein M. (Microbial infection) Interacts with Measles virus protein M. (Microbial infection) Interacts with Hendra virus protein M; this interaction promotes nuclear localization of M. (Microbial infection) Interacts with influenza virus B protein PB2; this interaction strongly supports influenza B virus replication. Accumulates in the nuclei at the S phase. Lacks a nuclear localization signal. Expressed in heart, lung, pancreas, prostate and in spleen, thymus and placenta. Histone binding is mediated by the concave surface of the LRR region. Some glutamate residues are glycylated by TTLL8. This modification occurs exclusively on glutamate residues and results in a glycine chain on the gamma-carboxyl group (By similarity). Directly cleaved by caspase-3/CASP3. No canonical donor splice site. Belongs to the ANP32 family.