CRM1 (chromosome region maintenance 1 protein homolog) mediates the nuclear export of cellular proteins (cargoes) bearing a leucine-rich nuclear export signal (NES) and of RNAs. In the nucleus, in association with RANBP3, CRM1 binds cooperatively to the NES on its target protein and to the GTPase Ran in its active GTP-bound form. Docking of this complex to the nuclear pore complex (NPC) is mediated through binding to nucleoporins. Upon transit of a nuclear export complex into the cytoplasm, disassembling of the complex and hydrolysis of Ran-GTP to Ran-GDP (induced by RANBP1 and RANGAP1, respectively) cause release of the cargo from the export receptor. The direction of nuclear export is thought to be conferred by an asymmetric distribution of the GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus. CRM1 also mediates the nuclear export of the Rev protein of HIV-1 and Rex protein of HTLV-1. It is involved in Rex dimerization, U3 snoRNA transport from Cajal bodies to nucleoli.
 

CRM1 is also involved in the control of several cellular processes by controlling the localization of cyclin B, MPAK, and MAPKAP kinase 2. CRM1 is also involved in the regulation NFAT and AP-1.