title: The Functional Role of eL19 and eB12 Intersubunit Bridge in the Eukaryotic Ribosome.
abstract: During translation, the two eukaryotic ribosomal subunits remain associated through 17 intersubunit bridges, five of which are eukaryote specific. These are mainly localized to the peripheral regions and are believed to stabilize the structure of the ribosome. The functional importance of these bridges remains largely unknown. Here, the essentiality of the eukaryote-specific bridge eB12 has been investigated. The main component of this bridge is ribosomal protein eL19 that is composed of an N-terminal globular domain, a middle region, and a long C-terminal α-helix. The analysis of deletion mutants demonstrated that the globular domain and middle region of eL19 are essential for cell viability, most likely functioning in ribosome assembly. The eB12 bridge, formed by contacts between the C-terminal α-helix of eL19 and 18S rRNA in concert with additional stabilizing interactions involving either eS7 or uS17, is dispensable for viability. Nevertheless, eL19 mutants impaired in eB12 bridge formation displayed slow growth phenotypes, altered sensitivity/resistance to translational inhibitors, and enhanced hyperosmotic stress tolerance. Biochemical analyses determined that the eB12 bridge contributes to the stability of ribosome subunit interactions in vitro. 60S subunits containing eL19 variants defective in eB12 bridge formation failed to form 80S ribosomes regardless of Mg(2+) concentration. The reassociation of 40S and mutant 60S subunits was markedly improved in the presence of deacetylated tRNA, emphasizing the importance of tRNAs during the subunit association. We propose that the eB12 bridge plays an important role in subunit joining and in optimizing ribosome functionality.
authors.affiliation: Institute of Molecular and Cell Biology, University of Tartu, Tartu 51010, Estonia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Kisly
authors.affiliation: Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, United States.
authors.forename: Suna P
authors.initials: SP
authors.lastname: Gulay
authors.affiliation: Institute of Chemistry, University of Tartu, Tartu 50411, Estonia.
authors.forename: Uno
authors.initials: U
authors.lastname: Mäeorg
authors.affiliation: Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, United States.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Dinman
authors.affiliation: Institute of Molecular and Cell Biology, University of Tartu, Tartu 51010, Estonia. Electronic address: jremme@ut.ee.
authors.forename: Jaanus
authors.initials: J
authors.lastname: Remme
authors.affiliation: Institute of Molecular and Cell Biology, University of Tartu, Tartu 51010, Estonia. Electronic address: ttamm@ut.ee.
authors.forename: Tiina
authors.initials: T
authors.lastname: Tamm
mesh_terms: D005057:Eukaryotic Cells / Q000502:physiology*; D009154:Mutation / Q000235:genetics; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis / Q000235:genetics / Q000502:physiology; D012335:RNA, Ribosomal / Q000235:genetics; D012343:RNA, Transfer / Q000235:genetics; D012269:Ribosomal Proteins / Q000235:genetics; D054657:Ribosome Subunits / Q000235:genetics / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000502:physiology
chemical_list: D012335:RNA, Ribosomal; D012269:Ribosomal Proteins; D012343:RNA, Transfer
keywords: Saccharomyces cerevisiae; eukaryote-specific bridges; ribosome assembly; ribosome subunit association; stress tolerance