GTPase activator for RAN, converting it to the GDP-bound state (PubMed:9108047). Converts cytoplasmic GTP-bound RAN to GDP-bound RAN, which is required for RAN-mediated nuclear import and export (By similarity). Homodimer (By similarity). Identified in a complex with RANBP2 and the ubiquitin-conjugating enzyme E2 (UBE2I) (PubMed:9108047). Cytoplasmic during interphase. Detected at the nuclear envelope during interphase. Targeted to the nuclear pores after sumoylation. During mitosis, associates with mitotic spindles, but is essentially not detected at the spindle poles. Mitotic location also requires sumoylation. May be sumoylated. Belongs to the RNA1 family.