title: Over expression of a tRNA(Leu) isoacceptor changes charging pattern of leucine tRNAs and reveals new codon reading.
abstract: During mRNA translation, synonymous codons for one amino acid are often read by different isoaccepting tRNAs. The theory of selective tRNA charging predicts greatly varying percentages of aminoacylation among isoacceptors in cells starved for their common amino acid. It also predicts major changes in tRNA charging patterns upon concentration changes of single isoacceptors, which suggests a novel type of translational control of gene expression. We therefore tested the theory by measuring with Northern blots the charging of Leu-tRNAs in Escherichia coli under Leu limitation in response to over expression of tRNA(GAG)(Leu). As predicted, the charged level of tRNA(GAG)(Leu) increased and the charged levels of four other Leu isoacceptors decreased or remained unchanged, but the charged level of tRNA(UAG)(Leu) increased unexpectedly. To remove this apparent inconsistency between theory and experiment we postulated a previously unknown common codon for tRNA(GAG)(Leu) and tRNA(UAG)(Leu). Subsequently, we demonstrated that the tRNA(GAG)(Leu) codon CUU is, in fact, read also by tRNA(UAG)(Leu), due to a uridine-5-oxyacetic acid modification.
authors.affiliation: Department of Molecular Cell Biology, University of Copenhagen, DK-1353 Copenhagen, Denmark.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Sørensen
authors.forename: Johan
authors.initials: J
authors.lastname: Elf
authors.forename: Elli
authors.initials: E
authors.lastname: Bouakaz
authors.forename: Tanel
authors.initials: T
authors.lastname: Tenson
authors.forename: Suparna
authors.initials: S
authors.lastname: Sanyal
authors.forename: Glenn R
authors.initials: GR
authors.lastname: Björk
authors.forename: Måns
authors.initials: M
authors.lastname: Ehrenberg
mesh_terms: D000926:Anticodon / Q000737:chemistry; D015152:Blotting, Northern; D003062:Codon / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics*; D014176:Protein Biosynthesis; D012346:RNA, Transfer, Amino Acyl / Q000235:genetics / Q000378:metabolism*; D012356:RNA, Transfer, Leu / Q000235:genetics / Q000378:metabolism*
chemical_list: D000926:Anticodon; D003062:Codon; D012346:RNA, Transfer, Amino Acyl; D012356:RNA, Transfer, Leu