Functions in nuclear protein import as an adapter protein fornuclear receptor KPNB1. Binds specifically and directly to substratescontaining either a simple or bipartite NLS motif. Docking of theimportin/substrate complex to the nuclear pore complex (NPC) ismediated by KPNB1 through binding to nucleoporin FxFG repeats and thecomplex is subsequently translocated through the pore by an energyrequiring, Ran-dependent mechanism. At the nucleoplasmic side of theNPC, Ran binds to importin-beta and the three components separate andimportin-alpha and -beta are re-exported from the nucleus to thecytoplasm where GTP hydrolysis releases Ran from importin. Thedirectionality of nuclear import is thought to be conferred by anasymmetric distribution of the GTP- and GDP-bound forms of Ran betweenthe cytoplasm and nucleus.

MSTNENANTPAARLHRFKNKGKDSTEMRRRRIEVNVELRKAKKDDQMLKRRNVSSFPDDATSPLQENRNNQGTVNWSVDDIVKGINSSNVENQLQATQAARKLLSREKQPPIDNIIRAGLIPKFVSFLGRTDCSPIQFESAWALTNIASGTSEQTKAVVDGGAIPAFISLLASPHAHISEQAVWALGNIAGDGSVFRDLVIKYGAVDPLLALLAVPDMSSLACGYLRNLTWTLSNLCRNKNPAPPIDAVEQILPTLVRLLHHDDPEVLADTCWAISYLTDGPNERIGMVVKTGVVPQLVKLLGASELPIVTPALRAIGNIVTGTDEQTQVVIDAGALAVFPSLLTNPKTNIQKEATWTMSNITAGRQDQIQQVVNHGLVPFLVSVLSKADFKTQKEAVWAVTNYTSGGTVEQIVYLVHCGIIEPLMNLLTAKDTKIILVILDAISNIFQAAEKLGETEKLSIMIEECGGLDKIEALQNHENESVYKASLSLIEKYFSVEEEEDQNVVPETTSEGYTFQVQDGAPGTFNF