GTPase involved in nucleocytoplasmic transport, participating both to the import and the export from the nucleus of proteins and RNAs. Switches between a cytoplasmic GDP- and a nuclear GTP-bound state by nucleotide exchange and GTP hydrolysis. Nuclear import receptors such as importin beta bind their substrates only in the absence of GTP-bound RAN and release them upon direct interaction with GTP-bound RAN, while export receptors behave in the opposite way. Thereby, RAN controls cargo loading and release by transport receptors in the proper compartment and ensures the directionality of the transport. Interaction with RANBP1 induces a conformation change in the complex formed by XPO1 and RAN that triggers the release of the nuclear export signal of cargo proteins. RAN (GTP-bound form) triggers microtubule assembly at mitotic chromosomes and is required for normal mitotic spindle assembly and chromosome segregation. Required for normal progress through mitosis (By similarity). GTP-bound Ran modulates both spindle and nuclear envelope assembly, supporting a role during mitosis (PubMed:12121620). During oogenesis, modulates formation of Nup358-containing granules and biogenesis of the nuclear pore complex probably by mediating the transport of their components along microtubules (PubMed:31626769). Mg(2+) interacts primarily with the phosphate groups of the bound guanine nucleotide. Found in a nuclear export complex with RanGTP, exportin and pre-miRNA (By similarity). Interacts with tamo (PubMed:12653959). Localizes around the microtubule spindle during mitosis. Belongs to the small GTPase superfamily. Ran family.