Binds to conventional NLS motifs and mediates nuclear protein import across the nuclear envelope. Acts as cellular receptor for the nuclear import of the virD2 protein of Agrobacterium and is essential for Agrobacterium-mediated root transformation. Forms a complex with importin subunit beta-1 (By similarity). Interacts with A.tumefaciens VirD2 and VirE2 (PubMed:18836040). Belongs to the importin alpha family.