title: Cytosolic Hsp70 and co-chaperones constitute a novel system for tRNA import into the nucleus.
abstract: tRNAs are unique among various RNAs in that they shuttle between the nucleus and the cytoplasm, and their localization is regulated by nutrient conditions. Although nuclear export of tRNAs has been well documented, the import machinery is poorly understood. Here, we identified Ssa2p, a major cytoplasmic Hsp70 in Saccharomyces cerevisiae, as a tRNA-binding protein whose deletion compromises nuclear accumulation of tRNAs upon nutrient starvation. Ssa2p recognizes several structural features of tRNAs through its nucleotide-binding domain, but prefers loosely-folded tRNAs, suggesting that Ssa2p has a chaperone-like activity for RNAs. Ssa2p also binds Nup116, one of the yeast nucleoporins. Sis1p and Ydj1p, cytoplasmic co-chaperones for Ssa proteins, were also found to contribute to the tRNA import. These results unveil a novel function of the Ssa2p system as a tRNA carrier for nuclear import by a novel mode of substrate recognition. Such Ssa2p-mediated tRNA import likely contributes to quality control of cytosolic tRNAs.
authors: Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan.
authors: Akira
authors: A
authors: Takano
authors: Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan.
authors: Takuya
authors: T
authors: Kajita
authors: Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan.
authors: Makoto
authors: M
authors: Mochizuki
authors: Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan.
authors: Toshiya
authors: T
authors: Endo
authors: Graduate School of Life Science, University of Hyogo, Kobe, Japan.
authors: Tohru
authors: T
authors: Yoshihisa
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D050956:HSP40 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D028861:Nuclear Pore Complex Proteins / Q000235:genetics / Q000378:metabolism; D009690:Nucleic Acid Conformation; D010766:Phosphorylation; D011485:Protein Binding; D034443:RNA Transport / Q000235:genetics; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C077730:NUP116 protein, S cerevisiae; D028861:Nuclear Pore Complex Proteins; C070320:SIS1 protein, S cerevisiae; C542288:SSA2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C070319:YDJ1 protein, S cerevisiae; D012343:RNA, Transfer
keywords: Hsp70; S. cerevisiae; cell biology; chaperone; nuclear import; tRNA