Binds specifically and directly to substrates containing either a simple or bipartite NLS motif. Promotes docking of import substrates to the nuclear envelope. Seems to act as a cytosolic receptor for both simple and bipartite NLS motifs (By similarity). It is required for normal cell proliferation and may serve as an adapter molecule to form complexes with other proteins. May act as a tumor suppressor in hematopoietic cells. May play a role in the nuclear import of karyophilic proteins and some of these may be required for the normal transmission and function of proliferative signals in the cells. Forms a complex with importin beta subunit. Shuttles between the cytoplasm and nucleus in a cell cycle-dependent manner. Predominantly expressed in the neuroblast stem cells. High levels are detected during the first half of embryogenesis reaching a maximum between 4 and 8 hours of development. Protein expression increases again from the third larval instar onwards. It is expressed in a maternal/early embryonic phase, and again during morphogenesis in late larval and pupal stages. Belongs to the importin alpha family. Was originally thought to be the overgrown hematopoietic organs-31 protein (OHO-31). Wrong choice of frame.