Fig. 7. Scheme for the interactions of Imp13 with RanGTP, its export substrate eIF1A and an import cargo. Under cytoplasmic conditions, RanBP1/RanBP2 and RanGAP remove RanGTP from Imp13. This is insufficient to release eIF1A from Imp13, but allows a displacement of eIF1A by import substrates. The Imp13–import substrate complex can then enter nuclei. In a nuclear environment, the import substrate is displaced by RanGTP, which in turn favours the eIF1A–Imp13 interaction and thereby allows eIF1A export.