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Description

Exportin-1 (UniProt O14980, also known as Chromosome region maintenance 1 protein homolog, CRM1 homolog, Exp1) is encoded by the XPO1 (also known as CRM1) gene (Gene ID 7514) in human. The transport of macromolecules between cytoplasm and nucleus is mediated by importins and exportins and regulated by the small GTPase Ran. Most nuclear importins & exportins, including exportin-1, belong to the beta-karyopherin (KAP) family of proteins, Importins bind their cargoes with either nuclear localization signal (NLS) or M9 domain-containing hnRNP proteins in the cytoplasm, while exportins target their substrates via their nuclear export signal (NES) or M9 domain inside the nucleus. The energy dependence of nucleocytoplasmic transport replies on the Ran GTPase system, where the nucleotide exchange factor (NEF) RCC1/Prp20p, the GTPase activating protein (GAP) RanGAP1/Rna1p, and the Ran binding protein (RBP) RanBP1/Yrb1p are arranged asymmetrically to produce a high Ran GTP:Ran GDP ratio in the nucleus and the reverse ratio in the cytoplasm. Exportin 1/CRM1 is reported to bind RanGTP and either Rev or PKI NES peptides in a cooperative manner in vitro and exogenous expression of human CRM1 in Xenopus oocytes is shown to increase the rate of Rev and U snRNA nuclear export.