GTPase activator for RAN (PubMed:8146159, PubMed:8896452, PubMed:16428860). Converts cytoplasmic GTP-bound RAN to GDP-bound RAN, which is essential for RAN-mediated nuclear import and export (PubMed:8896452, PubMed:27160050). Mediates dissociation of cargo from nuclear export complexes containing XPO1, RAN and RANBP2 after nuclear export (PubMed:27160050). Homodimer (PubMed:8146159). Interacts with RAN (PubMed:7891706, PubMed:8896452, PubMed:16428860). Forms a complex with RANBP2/NUP358, NXF1 and NXT1 (PubMed:14729961). Forms a tight complex in association with RANBP2/NUP358 and UBE2I/UBC9, the ubiquitin-conjugating enzyme E2 (PubMed:15037602, PubMed:27160050, PubMed:15931224, PubMed:22194619). Interacts with UBE2I; the interaction conjugates SUMO1 to RANGAP1, and subsequently stabilizes interactions of sumoylated RANGAP1 with RANBP2/NUP358 (PubMed:15037602, PubMed:27160050, PubMed:15931224). The complex composed of RANBP2, SUMO1, RANGAP1 and UBE2I associates with nuclear pore complexes (PubMed:15037602, PubMed:15931224). Identified in a complex composed of RAN, RANBP2, sumoylated RANGAP1, UBE2I and XPO1 (PubMed:27160050). Identified in a complex composed of RAN, RANGAP1 and RANBP1 (PubMed:16428860). Interacts with TRAF6 (PubMed:18093978). Interacts with SUMO1 and SENP1 (PubMed:17099698). Interacts (when sumoylated) with MYCBP2; interaction inhibits MYCBP2 E3 ubiquitin-protein ligase activity and promotes MYCBP2 translocation to the nucleus (PubMed:26304119). Cytoplasmic during interphase. Detected at the nuclear envelope during interphase (PubMed:11854305, PubMed:15037602). Targeted to the nuclear pores after sumoylation (PubMed:11854305). During mitosis, associates with mitotic spindles, but is essentially not detected at the spindle poles (PubMed:11854305, PubMed:15037602). Association with kinetochores appears soon after nuclear envelope breakdown and persists until late anaphase (PubMed:11854305). Mitotic location also requires sumoylation (PubMed:11854305). Highly expressed in brain, thymus and testis. Phosphorylation occurs before nuclear envelope breakdown and continues throughout mitosis. Phosphorylated by the M-phase kinase cyclin B/Cdk1, in vitro. Differential timimg of dephosphorylation occurs during phases of mitosis. The phosphorylated form remains associated with RANBP2/NUP358 and the SUMO E2-conjugating enzyme, UBE2I, on nuclear pore complex (NPC) diassembly and during mitosis. Sumoylated (PubMed:11854305, PubMed:15037602, PubMed:26304119, PubMed:27160050). Sumoylation is necessary for targeting to the nuclear envelope (NE), and for association with mitotic spindles and kinetochores during mitosis (PubMed:11854305). Also required for interaction with RANBP2 and is mediated by UBE2I (PubMed:27160050). Desumoylated by HINT1 (By similarity). Belongs to the RNA1 family.