Importin-β family proteins are nucleocytoplasmic transport receptors that import and export proteins and RNAs through the nuclear pores. In some import/export pathways, importin-β directly interacts with the cargo. For cargo containing a classical nuclear localization (cNLS) signal, importin-α acts as an adaptor linking the cargo to importin-β. (Adapted from FBrf0235243, FBrf0131350 and PMID:21029754).