title: The modification of the wobble base of tRNAGlu modulates the translation rate of glutamic acid codons in vivo.
abstract: In Escherichia coli, uridine in the wobble position of tRNAGlu and tRNALys is modified to mnm5s2U34. This modification is believed to restrict the base-pairing capability, i.e. to prevent misreading of near-cognate codons and reduce the efficiency of cognate codon reading, especially of codons ending in G. We have determined the influence of the 5-methylaminomethyl and the 2-thio modifications of mnm5s2U34 in tRNAGlu on the translation rate of the glutamate codons GAA and GAG in vivo. In wild-type cells, GAG is translated slower (7. 7 codons/second) and GAA faster (18 codons/second) than the average codon (13 codons/second). Surprisingly, tRNAGlu lacking the 5-methylaminomethyl group, thus containing s2U34, translated GAA twofold faster (47 codons/second) and GAG fourfold slower (1.9 codons/second) than fully modified tRNAGlu. In contrast, tRNAGlu that contains mnm5U34 instead of mnm5s2U34 translated GAA fourfold slower (4.5 codons/second) and GAG only 20% slower (6.2 codons/second). Clearly, the 5-methylaminomethyl group of mnm5s2U34 facilitates base-pairing with G while decreasing base-pairing with A, resulting in rates of translation of GAG and GAA that approach that of the average codon. The 2-thio group increases the recognition of GAA and has only a minor effect on the decoding of GAG. Furthermore, the 2-thio group is important for aminoacylation (see the accompanying paper). These data imply that the function of mnm5s2U34 may be different from what has been suggested previously.
authors.affiliation: Department of Molecular Cell Biology, University of Copenhagen, Denmark.
authors.forename: M K
authors.initials: MK
authors.lastname: Krüger
authors.forename: S
authors.initials: S
authors.lastname: Pedersen
authors.forename: T G
authors.initials: TG
authors.lastname: Hagervall
authors.forename: M A
authors.initials: MA
authors.lastname: Sørensen
mesh_terms: D003062:Codon; D018698:Glutamic Acid / Q000235:genetics*; D007700:Kinetics; D010441:Peptide Chain Elongation, Translational / Q000235:genetics*; D012352:RNA, Transfer, Glu / Q000737:chemistry*; D001616:beta-Galactosidase / Q000737:chemistry
chemical_list: D003062:Codon; D012352:RNA, Transfer, Glu; D018698:Glutamic Acid; D001616:beta-Galactosidase