Targeting of Ran: variation on a common theme?

The Ran GTPase plays a key role in nucleocytoplasmic transport. In its GTP- bound form, it directly interacts with members of the importin beta family of nuclear transport receptors and modulates their association with cargo. Work in cell-free higher-eukaryote systems has demonstrated additional role s for Ran in spindle and nuclear envelope formation during mitosis. However , until recently, no Ran-target proteins in these cellular processes were k nown. Several groups have now identified importin beta as one important tar get of Ran during mitotic spindle formation. This finding suggests that Ran uses the same effectors to regulate different cellular processes.