Ran GTPase system comprises ran-1, ran-2 and ran-3 and is essential in nucleocytoplasmic transport. Ran-1 is a GTP-binding protein that mediates the interaction between mitotic chromosomes and kinetochore microtubules. Plays a crucial role in nuclear envelope assembly at the end of each cell division. Required for the import of protein into the nucleus and also for RNA export. RCC1 (ran-3)/Ran (ran-1) complex (together with other proteins) acts as a component of a signal transmission pathway that detects unreplicated DNA. Found in a nuclear export complex with RanGTP, exportin and pre-miRNA (By similarity). At interphase, ran-1 is localized to the nucleus and the nuclear envelope. At prometaphase, ran-1 is still localized to the nuclear envelope. When the nuclear envelope begins to disassemble at M phase (early metaphase), ran-1 is localized throughout the entire cell. At late metaphase, ran-1 localizes to the kinetochore regions, this persists until anaphase. At telophase, ran-1 is localized around the decondensing chromosomes. Loss of ran-1 results in failure of correct attachment of kinetochore microtubules to mitotic chromosomes and the resultant loss of correct chromosome segregation. The number and the location of centrosomes are normal, and astral mictrotubules also seem unaffected. Nuclear envelope is not reestablished at the end of each cell division. Belongs to the small GTPase superfamily. Ran family.