EXPORTIN-1 (CRM1P) IS AN ESSENTIAL NUCLEAR EXPORT FACTOR

Nuclear protein export is mediated by nuclear export signals (NESs), b ut the mechanisms governing this transport process are not well unders tood. Using a novel protein export assay in S. cerevisiae, we identify CRM1 as an essential mediator of nuclear protein export in yeast. Crm 1p shows homology to importin beta-like transport factors and is able to specifically interact with both the NES motif and the Ran GTPase. A mutation in the shuttling protein Crm1p affects not only protein expo rt, but also mRNA export, indicating that these pathways are tightly c oupled in S. cerevisiae. The presented data are consistent with the co nclusion that Crm1p is a carrier for the NES-mediated protein export p athway. We propose CRM1 be renamed exportin 1 (XPO1).