Binds to conventional NLS motifs with high affinity in the absence of an importin beta subunit. Mediates nuclear protein import across the nuclear envelope in vitro in the absence of exogenously added importin beta subunit (PubMed:10428841). Acts as cellular receptor for the nuclear import of the virD2 protein of Agrobacterium, but is not essential for Agrobacterium-mediated root transformation (PubMed:18836040). Forms a complex with the importin subunit beta-1 KPNB1 (PubMed:10428841, PubMed:23582042). Interacts with VIP1 and promotes its nuclear import (PubMed:12124400). Interacts with A.tumefaciens VirD2 and VirE2 (PubMed:18836040). Belongs to the importin alpha family.