KPNA4 (karyopherin alpha 4), also known as importin alpha 3, is a member of the importin alpha family of proteins which includes KPNA1 (importin alpha 5), KPNA2 (importin alpha 1), KPNA3 (importin alpha 4), KPNA4 (importin alpha 3), KPNA5 (importin alpha 6), and KPNA6 (importin alpha 7). The importin alpha family of proteins plays a role in the import of proteins from the cytoplasm to the nucleus. The import of proteins from the cytoplasm to the nucleus involves docking the protein to receptors associated with the nuclear pore complex (NPC) followed by translocation through the nuclear pore. Importin alpha proteins bind the nuclear localization signal (NLS) of cargo proteins and function as adaptor proteins for the nuclear pore receptor KPNB1 (importin beta 1). KPNB1 is responsible for docking the importin-cargo complex to the cytoplasmic side of the NPC for its translocation through the NPC. KPNA3 (Importin alpha 4) and KPNA4 (importin alpha 3) have been reported to mediate the nuclear import of TNF-alpha induced nuclear import of NF-kappaB p50/p65 heterodimers. RNA interference experiments have shown that KPNA4 is important for HeLa cell proliferation and the nuclear import of the Ran guanine nucleotide exchange factor, RCC1.