Alternative titles; symbols
HGNC Approved Gene Symbol: XPOT
Cytogenetic location: 12q14.2 Genomic coordinates (GRCh38) : 12:64,404,392-64,451,125 (from NCBI)
Arts et al. (1998) and Kutay et al. (1998) independently identified XPOT, which they called exportin(tRNA), or exportin-t. Arts et al. (1998) reported that XPOT contains 960 amino acids, and Kutay et al. (1998) reported that XPOT contains 963 amino acids.
In eukaryotes, tRNAs are synthesized in the nucleus and after several maturation steps exported to the cytoplasm. Arts et al. (1998) and Kutay et al. (1998) independently identified exportin-t as a specific mediator of tRNA export. Exportin-t is a RanGTP-binding, importin beta-related factor with predominantly nuclear localization. It shuttles rapidly between nucleus and cytoplasm and interacts with nuclear pore complexes. Exportin-t binds tRNA directly and with high affinity. Its cellular concentration in Xenopus oocytes was found to be rate-limiting for export of all tRNAs tested, as judged by microinjection experiments. RanGTP regulates the substrate-exportin-t interaction such that tRNA can be preferentially bound in the nucleus and released in the cytoplasm.
Crystal Structure
Cook et al. (2009) reported the 3.2-angstrom resolution structure of Schizosaccharomyces pombe Xpot in complex with tRNA and RanGTP, and the 3.1-angstrom structure of unbound Xpot, revealing both nuclear and cytosolic snapshots of this transport factor. Xpot undergoes a large conformational change on binding cargo, wrapping around the tRNA and, in particular, binding to the tRNA 5- and 3-prime ends. The binding mode explains how Xpot can recognize all mature tRNAs in the cell and yet distinguish them from those that have not been properly processed, thus coupling tRNA export to quality control.
Gross (2013) mapped the XPOT gene to chromosome 12q14.2 based on an alignment of the XPOT sequence (GenBank AF039022) with the genomic sequence (GRCh37).
Arts, G.-J., Fornerod, M., Mattaj, I. W. Identification of a nuclear export receptor for tRNA. Curr. Biol. 8: 305-314, 1998. [PubMed: 9512417] [Full Text: https://doi.org/10.1016/s0960-9822(98)70130-7]
Cook, A. G., Fukuhara, N., Jinek, M., Conti, E. Structures of the tRNA export factor in the nuclear and cytosolic states. Nature 461: 60-65, 2009. [PubMed: 19680239] [Full Text: https://doi.org/10.1038/nature08394]
Gross, M. B. Personal Communication. Baltimore, Md. 3/28/2013.
Kutay, U., Lipowsky, G., Izaurralde, E,, Bischoff, F. R., Schwarzmaier, P., Hartmann, E., Gorlich, D. Identification of a tRNA-specific nuclear export receptor. Molec. Cell 1: 359-369, 1998. [PubMed: 9660920] [Full Text: https://doi.org/10.1016/s1097-2765(00)80036-2]