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Gene Review

LOS1  -  Los1p

Saccharomyces cerevisiae S288c

Synonyms: Exportin(tRNA), Exportin-T, Karyopherin-beta, YKL205W, tRNA exportin
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Disease relevance of LOS1


High impact information on LOS1

  • Interestingly, various proteins involved in nuclear-cytoplasmic traffic, such as exportins Cse1p, Mex67p, and Los1p, exhibit a robust BA [2].
  • 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 [3].
  • Los1p was shown previously to be required for efficient pre-tRNA splicing; we report here that Los1p localizes to the nuclear pores and is linked functionally to several components of the tRNA biogenesis machinery including Pus1p and Tfc4p [4].
  • Arc1p was found in a screen for components that interact genetically with Los1p, a nuclear pore-associated yeast protein involved in tRNA biogenesis [5].
  • The Ran-GTP-binding exportin, Los1p/Xpo-t, and additional pathway(s) mediate tRNA transport to the cytoplasm [6].

Biological context of LOS1

  • Because LOS1 is unessential in yeast, other pathways for tRNA nuclear export must exist [7].
  • Disruption or deletion of most of the LOS1 gene was not lethal; cells carrying the disrupted los1 alleles were viable and had phenotypes similar to those of cells carrying the los1-1 allele [8].
  • Integration of plasmid DNA at the LOS1 locus confirmed that these clones contained authentic LOS1 sequences [8].
  • The 12CA5 antibody recognizes an epitope-tagged protein of the size predicted by the LOS1 open reading frame [1].
  • Furthermore, overexpression of full-length or N-terminally truncated Los1p was shown to have dominant-negative effects on cell growth and different nuclear export pathways [9].

Anatomical context of LOS1

  • We propose that LOS1 mutations may affect pre-tRNA processing via alteration of the nuclear matrix [1].
  • Los1p, the Saccharomyces cerevisiae exportin-t homologue, binds tRNA and functions in pre-tRNA splicing and export of mature tRNA from the nucleus to the cytosol [7].

Associations of LOS1 with chemical compounds

  • Los1p cannot be extracted from nuclei by treatment with nucleases, salts, or Triton X-100 [1].

Physical interactions of LOS1

  • In a two-hybrid screen, we identified Nup2p as a nucleoporin interacting with Los1p [9].

Regulatory relationships of LOS1


Other interactions of LOS1

  • Because LOS1 is nonessential, tRNA export in vertebrate and yeast cells likely involves factors in addition to exportin-t. Mutation of RNA1, which encodes RanGAP, causes nuclear accumulation of tRNAs and poly(A) RNA [11].
  • Overproduced PUS4 appears to impede 5'-end processing or export of certain tRNAs in the nucleus in a manner remedied by increased expression of RNase P or LOS1, respectively [12].
  • SOL1, the founding member of the S. cerevisiae SOL family, was previously identified as a multi-copy suppressor of the los1 defect in tRNA-mediated nonsense suppression [13].
  • However, Sol4p does not act as a los1 multi-copy suppressor [13].
  • Saccharomyces cerevisiae Los1p, which is genetically linked to the nuclear pore protein Nsp1p and several tRNA biogenesis factors, was recently grouped into the family of importin/karyopherin-beta-like proteins on the basis of its sequence similarity [9].

Analytical, diagnostic and therapeutic context of LOS1


  1. The Saccharomyces cerevisiae LOS1 gene involved in pre-tRNA splicing encodes a nuclear protein that behaves as a component of the nuclear matrix. Shen, W.C., Selvakumar, D., Stanford, D.R., Hopper, A.K. J. Biol. Chem. (1993) [Pubmed]
  2. Chromatin boundaries in budding yeast: the nuclear pore connection. Ishii, K., Arib, G., Lin, C., Van Houwe, G., Laemmli, U.K. Cell (2002) [Pubmed]
  3. Cex1p is a novel cytoplasmic component of the Saccharomyces cerevisiae nuclear tRNA export machinery. McGuire, A.T., Mangroo, D. EMBO J. (2007) [Pubmed]
  4. Nuclear pore proteins are involved in the biogenesis of functional tRNA. Simos, G., Tekotte, H., Grosjean, H., Segref, A., Sharma, K., Tollervey, D., Hurt, E.C. EMBO J. (1996) [Pubmed]
  5. The yeast protein Arc1p binds to tRNA and functions as a cofactor for the methionyl- and glutamyl-tRNA synthetases. Simos, G., Segref, A., Fasiolo, F., Hellmuth, K., Shevchenko, A., Mann, M., Hurt, E.C. EMBO J. (1996) [Pubmed]
  6. Retrograde movement of tRNAs from the cytoplasm to the nucleus in Saccharomyces cerevisiae. Shaheen, H.H., Hopper, A.K. Proc. Natl. Acad. Sci. U.S.A. (2005) [Pubmed]
  7. A Los1p-independent pathway for nuclear export of intronless tRNAs in Saccharomycescerevisiae. Feng, W., Hopper, A.K. Proc. Natl. Acad. Sci. U.S.A. (2002) [Pubmed]
  8. Cloning and characterization of LOS1, a Saccharomyces cerevisiae gene that affects tRNA splicing. Hurt, D.J., Wang, S.S., Lin, Y.H., Hopper, A.K. Mol. Cell. Biol. (1987) [Pubmed]
  9. Yeast Los1p has properties of an exportin-like nucleocytoplasmic transport factor for tRNA. Hellmuth, K., Lau, D.M., Bischoff, F.R., Künzler, M., Hurt, E., Simos, G. Mol. Cell. Biol. (1998) [Pubmed]
  10. Los1p, involved in yeast pre-tRNA splicing, positively regulates members of the SOL gene family. Shen, W.C., Stanford, D.R., Hopper, A.K. Genetics (1996) [Pubmed]
  11. tRNA nuclear export in saccharomyces cerevisiae: in situ hybridization analysis. Sarkar, S., Hopper, A.K. Mol. Biol. Cell (1998) [Pubmed]
  12. Defects in tRNA processing and nuclear export induce GCN4 translation independently of phosphorylation of the alpha subunit of eukaryotic translation initiation factor 2. Qiu, H., Hu, C., Anderson, J., Björk, G.R., Sarkar, S., Hopper, A.K., Hinnebusch, A.G. Mol. Cell. Biol. (2000) [Pubmed]
  13. Division of labor among the yeast Sol proteins implicated in tRNA nuclear export and carbohydrate metabolism. Stanford, D.R., Whitney, M.L., Hurto, R.L., Eisaman, D.M., Shen, W.C., Hopper, A.K. Genetics (2004) [Pubmed]
  14. An aminoacylation-dependent nuclear tRNA export pathway in yeast. Grosshans, H., Hurt, E., Simos, G. Genes Dev. (2000) [Pubmed]
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