背景资料：Importin-9, also known as Imp9 or IPO9, is a 1,041 amino acid protein that contains one importin N-terminal domain and belongs to the Importin-∫ family. Localized to both the nucleus and the cytoplasm, Importin-9 functions as a nuclear transport receptor that mediates the docking of the Importin complex to the nuclear pore complex (NPC). Importin-9 mediates nuclear import of H2B histone, Ribosomal Protein S7 and Ribosomal Protein L18A. The gene encoding Importin-9 is located on human chromosome 1, the largest human chromosome that spans about 260 million base pairs and makes up 8% of the human genome.