title: Defects in transient tRNA translocation bypass tRNA synthetase quality control mechanisms.
abstract: Quality control mechanisms during protein synthesis are essential to fidelity and cell survival. Leucyl-tRNA synthetase (LeuRS) misactivates non-leucine amino acids including isoleucine, methionine, and norvaline. To prevent translational errors, mischarged tRNA products are translocated 30A from the canonical aminoacylation core to a hydrolytic editing-active site within a completely separate domain. Because it is transient, the tRNA translocation mechanism has been difficult to isolate. We have identified a "translocation peptide" within Escherichia coli LeuRS. Mutations in the translocation peptide cause tRNA to selectively bypass the editing-active site, resulting in mischarging that is lethal to the cell. This bypass mechanism also rescues aminoacylation of an editing site mutation that hydrolyzes correctly charged Leu-tRNA(Leu). Thus, these LeuRS mutants charge tRNA(Leu) but fail to translocate these products to the hydrolytic site, where they are cleared to guard against genetic code ambiguities.
authors.affiliation: Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois 61801, USA.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Hellmann
authors.forename: Susan A
authors.initials: SA
authors.lastname: Martinis
mesh_terms: D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases / Q000235:genetics* / Q000378:metabolism*; D001665:Binding Sites; D001692:Biological Transport; D002470:Cell Survival; D004926:Escherichia coli / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D017434:Protein Structure, Tertiary; D017393:RNA Editing; D012343:RNA, Transfer / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013824:Thermus / Q000378:metabolism
chemical_list: D010455:Peptides; D012343:RNA, Transfer; D000604:Amino Acyl-tRNA Synthetases