Functions in nuclear protein import via a substrate-importin alpha-beta transport complex that passes though the nuclear pore complexes (NPC). Binds specifically and directly to substrates containing either a simple or bipartite NLS motif (By similarity). Forms a complex with tnpo/importin subunit beta. The N-terminal hydrophilic region contains the importin beta binding domain (IBB domain), which is sufficient for binding importin beta and essential for nuclear protein import. Belongs to the importin alpha family. The gene for this protein is duplicated in strains AX3 and AX4. These strains contain a duplication of a segment of 750 kb of chromosome 2 compared to the corresponding sequence in strain AX2.