Functions in nuclear protein import, either in association with an adapter protein, like an importin-alpha subunit, which binds to nuclear localization signals (NLS) in cargo substrates, or by acting as autonomous nuclear transport receptor. Acting autonomously, serves itself as NLS receptor. Docking of the importin/substrate complex to the nuclear pore complex (NPC) is mediated by KPNB1 through binding to nucleoporin FxFG repeats and the complex is subsequently translocated through the pore by an energy requiring, Ran-dependent mechanism. At the nucleoplasmic side of the NPC, Ran binds to importin-beta and the three components separate and importin-alpha and -beta are re-exported from the nucleus to the cytoplasm where GTP hydrolysis releases Ran from importin. The directionality of nuclear import is thought to be conferred by an asymmetric distribution of the GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus. Mediates autonomously the nuclear import of ribosomal proteins RPL23A, RPS7 and RPL5 (PubMed:11682607). In association with IPO7, mediates the nuclear import of H1 histone. In vitro, mediates nuclear import of H2A, H2B, H3 and H4 histones. In case of HIV-1 infection, binds and mediates the nuclear import of HIV-1 Rev. Imports SNAI1 and PRKCI into the nucleus. Forms a complex with an importin alpha subunit (PubMed:8617227, PubMed:8692944). Interacts with XPO1 (PubMed:10209022). Forms a heterodimer with IPO7 (PubMed:9687515, PubMed:10228156, PubMed:10209022). The KPNB1/IPO7 heterodimer interacts with H1 histone (PubMed:10228156). Interacts with SNUPN (PubMed:9670026, PubMed:10209022, PubMed:18187419, PubMed:20476751). Interacts with H2A, H2B, H3 and H4 histones (By similarity). Component of an import snRNP complex composed of KPNB1, SNUPN, SMN1 and ZNF259 (PubMed:12095920). Component of a nuclear export receptor complex composed of KPNB1, Ran, SNUPN and XPO1 (PubMed:10209022, PubMed:10367892). Interacts with SRY (PubMed:12764225, PubMed:15297880). Interacts with PRKCI/atypical protein kinase C iota (PubMed:11891849). Interacts with KPNA2 (PubMed:10353244). Interacts with KPNA7 (PubMed:20701745). Interacts with SNAI1 (via zinc fingers) and SNAI2 (via zinc fingers) (PubMed:15836774, PubMed:19386897, PubMed:24699649). Interacts with SLC35G1 and STIM1 (PubMed:22084111). Interacts with DCAF8 (PubMed:22500989). Interacts with RAN (PubMed:10367892). Interacts with NUMA1 (via C-terminus); this interaction is inhibited by RanGTP (PubMed:11229403). Interacts with ZBED1/hDREF; required for nuclear import of ZBED1/hDREF (PubMed:17209048). Interacts with SRP19 (PubMed:11682607). Interacts with RPL23A (via BIB domain), RPS7 and RPL5 (PubMed:9687515, PubMed:11682607). Interacts with PARP16 (PubMed:22701565). (Microbial infection) Interacts with HIV-1 Rev and Tat. (Microbial infection) Interacts with HTLV-1 Rex. (Microbial infection) Interacts with human respiratory syncytial virus (HRSV) matrix protein; this interaction mediates nuclear import of the matrix protein early during infection. (Microbial infection) Part of a tetrameric complex composed of CRM1, importin alpha/beta dimer and the Venezuelan equine encephalitis virus (VEEV) capsid; this complex blocks the receptor-mediated transport through the nuclear pore. Mono-ADP-ribosylated by PARP16. Belongs to the importin beta family. Importin beta-1 subfamily.