The function of Ensembl gene identifier ENSG00000196497 (IPO4, importin 4) is as follows. Nuclear transport receptor that mediates nuclear import of proteins, such as histones, RPS3A, TNP2 and VDR (PubMed:11823430, PubMed:16207705, PubMed:17682055, PubMed:21454524, PubMed:30177573). Serves as receptor for nuclear localization signals (NLS) in cargo substrates (PubMed:11823430, PubMed:16207705). 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 (PubMed:11823430, PubMed:16207705). 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 (PubMed:11823430). 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 (PubMed:11823430). Mediates the nuclear import of the histone H3-H4 dimer when in complex with ASF1 (ASF1A or ASF1B) (PubMed:21454524, PubMed:29408485, PubMed:36103578). Also mediates the nuclear import of monomeric histones H3.1 and H4 (PubMed:30177573). Mediates the ligand-independent nuclear import of vitamin D receptor (VDR) (PubMed:16207705). In vitro, mediates the nuclear import of human cytomegalovirus UL84 by recognizing a non- classical NLS (PubMed:12610148). {ECO:0000269|PubMed:11823430, ECO:0000269|PubMed:12610148, ECO:0000269|PubMed:16207705, ECO:0000269|PubMed:17682055, ECO:0000269|PubMed:21454524, ECO:0000269|PubMed:29408485, ECO:0000269|PubMed:30177573, ECO:0000269|PubMed:36103578}.