Importin ß (karyopherin ß/PTAC97) forms a complex with importin a that is required for classical import of proteins across the nuclear envelope through the nuclear pore complex. Importin a acts as a bridge between the nuclear localization sequence (NLS) and importin ß, while importin ß is the site of initial docking to the pore and is responsible for transport of the target protein into the nucleus. Inside the nucleus, Ran-GTP binds to importin ß, resulting in dissociation of the ternary complex, and importin a and ß are independently recycled back into the cytoplasm. Recently some NLS-containing proteins have been shown to bind directly to importin ß and enter the nucleus in an importin a independent manner.Synonyms: Importin subunit beta-1, Importin-90, KPNB1, Nuclear factor P97