Ran is a monomeric GTPase present in all cells, it is involved in nuclear transport through NPC's. Ran can exist in two conformations, it can be bound to GTP or GDP. Ran-GTP is mainly found in the nucleus, whereas Ran-GDP is more concentrated in the cytosol. In the nucleus, Ran-GTP binding to import receptors bound to cargo on the nuclear side stimulates the release of cargo into the nucleus. After release, the import receptor bound to Ran-GTP is transported through the NPC to the cytoplasmic side, a regulatory protein Ran-GAP, stimulates hydrolysis of Ran-GTP to Ran-GDP in the cytoplasm.