Forskning ved Københavns Universitet - Københavns Universitet


The modification of the wobble base of tRNA(Glu) modulates the translation rate of glutamic acid codons in vivo

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In Escherichia coli, uridine in the wobble position of tRNA(Glu) and tRNA(Lys) 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 tRNA(Glu) the on 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, tRNA(Glu) 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 tRNA(Glu). In contrast, tRNA(Glu) 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.

TidsskriftJournal of Molecular Biology
Udgave nummer3
Sider (fra-til)621-631
Antal sider11
StatusUdgivet - 4 dec. 1998

ID: 222321853