title: Role of nuclear pools of aminoacyl-tRNA synthetases in tRNA nuclear export.
abstract: Reports of nuclear tRNA aminoacylation and its role in tRNA nuclear export (Lund and Dahlberg, 1998; Sarkar et al., 1999; Grosshans et al., 20001) have led to the prediction that there should be nuclear pools of aminoacyl-tRNA synthetases. We report that in budding yeast there are nuclear pools of tyrosyl-tRNA synthetase, Tys1p. By sequence alignments we predicted a Tys1p nuclear localization sequence and showed it to be sufficient for nuclear location of a passenger protein. Mutations of this nuclear localization sequence in endogenous Tys1p reduce nuclear Tys1p pools, indicating that the motif is also important for nucleus location. The mutations do not significantly affect catalytic activity, but they do cause defects in export of tRNAs to the cytosol. Despite export defects, the cells are viable, indicating that nuclear tRNA aminoacylation is not required for all tRNA nuclear export paths. Because the tRNA nuclear exportin, Los1p, is also unessential, we tested whether tRNA aminoacylation and Los1p operate in alternative tRNA nuclear export paths. No genetic interactions between aminoacyl-tRNA synthetases and Los1p were detected, indicating that tRNA nuclear aminoacylation and Los1p operate in the same export pathway or there are more than two pathways for tRNA nuclear export.
authors.affiliation: Department of Biochemistry and Molecular Biology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: A K
authors.initials: AK
authors.lastname: Azad
authors.forename: D R
authors.initials: DR
authors.lastname: Stanford
authors.forename: S
authors.initials: S
authors.lastname: Sarkar
authors.forename: A K
authors.initials: AK
authors.lastname: Hopper
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002458:Cell Fractionation; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D017930:Genes, Reporter / Q000235:genetics; D005816:Genetic Complementation Test; D006801:Humans; D015151:Immunoblotting; D017403:In Situ Hybridization; D008954:Models, Biological; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D028861:Nuclear Pore Complex Proteins; D012343:RNA, Transfer / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D014448:Tyrosine-tRNA Ligase / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D005656:Fungal Proteins; C408090:Los1 protein, S cerevisiae; D019913:Nuclear Localization Signals; D028861:Nuclear Pore Complex Proteins; D012346:RNA, Transfer, Amino Acyl; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D012343:RNA, Transfer; D014448:Tyrosine-tRNA Ligase