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. {ECO:0000269|PubMed:11909538}.