Nuclear transport factor (karyopherin) involved in protein transport between the cytoplasm and nucleoplasm. Required for the nuclear import of the complex composed the large subunit (TOA1) and the small subunit (TOA2) of the general transcription factor IIA (TFIIA). Required for the nuclear import of the RNR2-RNR4 heterodimer, also called beta-beta' subunit, which corresponds to the small subunit of the ribonucleotide reductase (RNR). May play a role in regulation of pleiotropic drug resistance. Associates with the nuclear pore complex (NPC). Interacts with GSP2, NUP1, NUP2, TOA1, TOA2 and WTM1. Present with 9760 molecules/cell in log phase SD medium. Belongs to the importin beta family.