Involved in nuclear protein import, either by acting as autonomous nuclear transport receptor or as an adapter-like protein in association with the importin-beta subunit KPNB1. Acting autonomously, may serve as receptor for nuclear localization signals (NLS) and promote translocation of import substrates through the nuclear pore complex (NPC) by an energy requiring, Ran-dependent mechanism. At the nucleoplasmic side of the NPC, Ran binds to importin, the importin/substrate complex dissociates and importin is re-exported from the nucleus to the cytoplasm where GTP hydrolysis releases Ran. 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. In vitro mediates the nuclear import of the signal recognition particle protein SRP19. May also be involved in cytoplasm-to-nucleus shuttling of a broad spectrum of other cargos, including Argonaute-microRNAs complexes, the JUN protein, RELA/NF-kappa-B p65 subunit, the translation initiation factor EIF4E and a set of receptor-activated mothers against decapentaplegic homolog (SMAD) transcription factors that play a critical role downstream of the large family of transforming growth factor beta and bone morphogenetic protein (BMP) cytokines. Forms a heterodimer with KPNB1. Interacts with SRP19. Interacts with RPL23A. Binds directly to nuclear pore complexes. Knockout animals present with reduced grip strength and diminished vertical activity. Progressive dilatation can be observed in the aortic root at the level of the sinuses of Valsalva and distal ascending aorta, and aneurysms of the distal ascending aorta are becoming visible at the age of 8-12 weeks. Generally, males are more severely affected, exhibiting larger aortas and experiencing dissection and/or rupture more frequently than females. Belongs to the importin beta family. The regions from 407 to 653 were deduced from the genomic sequence and ESTs by similarity to the human sequence.