importin beta-2 subunit (karyopherin beta-2 subunit, KPNB2, transportin-1, M9 region interaction protein, MIP, TNPO1, MIP1, TRN)

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Function

nuclear protein import as nuclear transport receptor
receptor for nuclear localization signals (NLS) in cargo substrates
thought to mediate docking of importin/substrate complex to the nuclear pore complex through binding to nucleoporin
the complex is subsequently translocated through the pore by an energy requiring, Ran-dependent mechanism
at the nucleoplasmic side of the nuclear pore complex, Ran binds to the importin, the importin/substrate complex dissociates & importin is re-exported from the nucleus to the cytoplasm where GTP hydrolysis releases Ran
directionality of nuclear import is thought to be conferred by an asymmetric distribution of the GTP- & GDP-bound forms of Ran between the cytoplasm & nucleus
involved in nuclear import of M9-containing proteins
in vitro, binds directly to the M9 region of the heterogeneous nuclear ribonucleoproteins (hnRNP), hnRNPA1 & hnRNPA2 & mediates their nuclear import
appears also to be involved in hnRNPA1 & hnRNPA2 nuclear export
mediates nuclear import of ribosomal proteins RPL23A, RPS7 & RPL5
binds to a beta-like import receptor binding (BIB) domain of RPL23A
in vitro, mediates nuclear import of H2A, H2B, H3 & H4 histones, & SRP19
binds HNRPA1, HNRPA2, HNRPDL, RPL23A, RPS7, RPL5, RAN & SRP19