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Updated: Jul 10, 2026
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Residue-specific Incorporation of Noncanonical Amino Acids into Model Proteins Using an Escherichia coli Cell-free Transcription-translation System
Published on: August 1, 2016
AUA codon decoding by preferential use of tRNAIle(UAU) in Lactobacillus casei
Chie Tomikawa1, Satoshi Okura2, Gakuto Uesugi2
1Ehime Daigaku tomikawa.chie.mm@ehime-u.ac.jp.
RNA (New York, N.Y.)
|July 8, 2026
Summary
Bacteria use specific transfer RNAs (tRNAs) to accurately read genetic code. This study reveals that tRNAIle(UAU) is preferentially used over tRNAIle(LAU) for isoleucine AUA codon decoding, highlighting a novel translational control mechanism.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Modified nucleosides in transfer RNA (tRNA) anticodons are crucial for accurate genetic code decoding.
- Bacterial isoleucine AUA codon decoding typically involves tRNAIle(LAU) with lysidine (L), ensuring discrimination from the methionine AUG codon.
- Some bacteria, like *Mycoplasma mobile*, use tRNAIle(UAU) with unmodified uridine for AUA decoding, avoiding AUG recognition.
Purpose of the Study:
- To investigate the roles of coexisting tRNAIle(LAU) and tRNAIle(UAU) in a lactic acid bacterium.
- To elucidate the mechanism of isoleucine AUA codon decoding and translational control in bacteria with dual tRNA isoacceptors.
Main Methods:
- *In vivo* aminoacylation assays to compare tRNAIle(LAU) and tRNAIle(UAU) utilization.
- *In vitro* aminoacylation assays to assess the effect of 4-thiouridine (s4U) modification on tRNAIle(UAU).
- Ribosomal A-site binding assays to evaluate codon discrimination by tRNAIle(LAU) and tRNAIle(UAU) with specific modifications.
Main Results:
- *In vivo*, tRNAIle(LAU) was scarcely aminoacylated, while tRNAIle(UAU) was efficiently aminoacylated.
- 4-thiouridine (s4U) at position 8 inhibited IleRS-dependent aminoacylation of tRNAIle(UAU) *in vitro*, suggesting a regulatory role for tRNA modification.
- tRNAIle(LAU) showed poor discrimination between AUA and AUG codons, whereas tRNAIle(UAU) with N6-threonylcarbamoyladenosine (t6A) at position 37 preferentially recognized AUA.
Conclusions:
- AUA codon decoding in this bacterium is primarily mediated by tRNAIle(UAU), not the canonical tRNAIle(LAU).
- Differential utilization of tRNA isoacceptors and tRNA modifications provide an alternative mechanism for codon decoding and translational control in bacteria.
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