nes signals were first discovered in the human immunodeficiency virus type 1 (hiv-1) rev protein and camp-dependent protein kinase inhibitor (pki). the karyopherin receptor crm1 has been identified as the export receptor for leucine-rich ness in several organisms and is an evolutionarily conserved protein. the export mediated by crm1 can be effectively inhibited by the fungicide leptomycin b (lmb), providing excellent experimental verification of this pathway.