RanBP3, a Ran-interacting nuclear protein, unlike the related proteins RanBP1 and RanBP2, which promote disassembly of the export complex in the cytosol, acts as a CRM1 cofactor, enhancing nuclear export signal (NES) export by stabilizing the export complex in the nucleus. CRM1/Exportin1 is responsible for exporting many proteins and ribonucleoproteins from the nucleus to the cytosol. RanBP3 also alters the cargo selectivity of CRM1, promoting recognition of the NES of HIV-1 Rev and of other cargos while deterring recognition of the import adaptor protein Snurportin1. RanBP3 contains a N-terminal nuclear localization signal (NLS), 2 FxFG motifs, and a single RanBD. RabBD shares structural similarity to the PH domain, but lacks detectable sequence similarity.