Improtins and exportins are regulated by Ran
	• Like other G proteins, Ran can switch between GTP-bound and GDP-bound states.  Transition from the GTP-bound to the GDP-bound state is catalyzed by a GTPase-activating protein (GAP) which induces hydrolysis of the bound GTP.  The reverse transition is catalyzed by guanine nucleotide exchange factor (GEF) which induces exchange between the bound GDP and the cellular GTP.