Definition:

Nuclear transport receptor that mediates nuclear import of proteins, such as histones, proteasome and actin. Serves as receptor for nuclear localization signals (NLS) in cargo substrates. Is thought to mediate docking of the importin/substrate complex to the nuclear pore complex (NPC) through binding to nucleoporin 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 the 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. Mediates the import of pre-assembled proteasomes into the nucleus; AKIRIN2 acts as a molecular bridge between IPO9 and the proteasome complex. Mediates the nuclear import of histones H2A, H2B, H4 and H4. In addition to nuclear import, also acts as a chaperone for histones by preventing inappropriate non-nucleosomal interactions. Mediates the nuclear import of actin (By similarity).