Cex1p is a novel cytoplasmic component of the Saccharomyces cerevisiae nuclear tRNA export machinery.

The Saccharomyces cerevisiae Yor112wp, which we named Cex1p, was identified using a yeast tRNA three-hybrid interaction approach and an in vivo nuclear tRNA export assay as a cytoplasmic component of the nuclear tRNA export machinery. Cex1p binds tRNA saturably, and associates with the nuclear pore complex by interacting directly with Nup116p. Cex1p co-purifies with the nuclear tRNA export receptors Los1p and Msn5p, the eukaryotic elongation factor eEF-1A, which delivers aminoacylated tRNAs to the ribosome, and the RanGTPase Gsp1p, but not with Cca1p, a tRNA maturation enzyme that facilitates translocation of non-aminoacylated tRNAs across the nuclear pore complex. Depletion of Cex1p and eEF-1A or Los1p significantly reduced the efficiency of nuclear tRNA export. Cex1p interacts with Los1p but not with eEF-1A in vitro. These findings suggest that Cex1p is a component of the nuclear aminoacylation-dependent tRNA export pathway in S. cerevisiae. They also suggest that Cex1p collects aminoacyl-tRNAs from the nuclear export receptors at the cytoplasmic side of the nuclear pore complex, and transfers them to eEF-1A using a channelling mechanism.