Cycling of Ran in nucleocytoplasmic transport
Ran is a member of the Ras family of small GTPases. Ran is an important component of many crucial nucleocytoplasmic transport pathways. The cycling of Ran is controlled by the RanGTP- RanGDP gradient established by the Ran Guanine nucleotide exchange Factor (RanGEF) RCC1 and the Ran GTPase-activating Protein (RanGAP). These two proteins combine to create a Ran gradient where RanGDP is predominantly cytoplasmic. RCC1 binds to chromatin and so RanGTP is found associated with DNA. RCC1 dissociated GDP from Ran and allows GTP to be bound. As Ran leaves the nucleus The two Ran binding proteins, RanBP1 and RanBP2 cooperate with RanGAP to induce GTP hydrolysis of Ran. There are several nuclear import factors that use the Ran gradient as part of their translocation mechanism
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REFERENCES: Kuersten S, Ohno M, Mattaj IW. Nucleocytoplasmic transport: Ran, beta and beyond. Trends Cell Biol. 2001 Dec;11(12):497-503. Review.
