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FIG. 1. HIV Rev exports unspliced viral mRNAs through the CRM1 export receptor. CRM1 is a member of the importin/exportin or karyopherin family of nuclear transport receptors (26, 70). Nucleocytoplasmic transport mediated by the importin/exportin family requires the small GTPase Ran. RanGTP concentrations are high in the nucleus, while RanGDP concentrations are high in the cytoplasm. Import of cargo requires binding to an importin. After translocation through the NPC, RanGTP in the nucleus dissociates the cargo from importin, which binds RanGTP to be recycled to the cytoplasm. Export from the nucleus requires binding of the cargo to a nuclear exportin, which binds RanGTP in a trimeric complex. In the cytoplasm, the Ran GTPase, RanGAP, converts RanGTP to RanGDP, resulting in the release of the cargo and the exportin (reviewed in reference 17). Rev binds to the highly structured RRE in unspliced HIV mRNA and interacts with CRM1 through its leucine-rich NES. This interaction can be blocked by LMB. CRM1 binds RanGTP and Rev, which is bound to the cargo RNA for translocation through the NPC.

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