IPO4
Description
The IPO4 (importin 4) is a protein-coding gene located on chromosome 14.
Importin-4 is a protein that in humans is encoded by the IPO4 gene.
Importin-4, also known as Importin-4b or Ran-binding protein 4, is a nuclear transport receptor involved in the nuclear import of proteins such as histones, RPS3A, TNP2, and VDR. It functions by recognizing nuclear localization signals (NLS) in cargo substrates and mediating their docking to the nuclear pore complex (NPC). This interaction is facilitated by binding to nucleoporin, and subsequent translocation through the pore is achieved through an energy-requiring, Ran-dependent mechanism. At the nucleoplasmic side of the NPC, Ran binds to Importin-4, leading to the dissociation of the Importin-4/substrate complex and the re-export of Importin-4 from the nucleus to the cytoplasm. This process is regulated by GTP hydrolysis, which releases Ran. The directionality of nuclear import is thought to be governed by an asymmetric distribution of GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus. Notably, Importin-4 mediates the nuclear import of the histone H3-H4 dimer when complexed with ASF1 (ASF1A or ASF1B) and the ligand-independent nuclear import of the vitamin D receptor (VDR). In vitro, Importin-4 has been shown to mediate the nuclear import of human cytomegalovirus UL84 by recognizing a non-classical NLS.
IPO4 is also known as Imp4.
