EMD-29821
Structure of the Escherichia coli 70S ribosome in complex with A-site tRNAIle(LAU) bound to the cognate AUA codon (Structure III)
EMD-29821
Single-particle2.8 Å
Deposition: 16/02/2023
Map released: 06/03/2024
Last modified: 25/12/2024
Sample Organism:
Escherichia coli,
Escherichia phage T4
Sample: Structure of the Escherichia coli 70S ribosome in complex with A-site tRNAIle(LAU) bound to the cognate AUA codon (Structure III)
Fitted models: 8g7r (Avg. Q-score: 0.534)
Raw data: EMPIAR-11584
Deposition Authors: Rybak MY , Gagnon MG
Sample: Structure of the Escherichia coli 70S ribosome in complex with A-site tRNAIle(LAU) bound to the cognate AUA codon (Structure III)
Fitted models: 8g7r (Avg. Q-score: 0.534)
Raw data: EMPIAR-11584
Deposition Authors: Rybak MY , Gagnon MG
Structures of the ribosome bound to EF-Tu-isoleucine tRNA elucidate the mechanism of AUG avoidance.
Abstract:
The frequency of errors upon decoding of messenger RNA by the bacterial ribosome is low, with one misreading event per 1 × 104 codons. In the universal genetic code, the AUN codon box specifies two amino acids, isoleucine and methionine. In bacteria and archaea, decoding specificity of the AUA and AUG codons relies on the wobble avoidance strategy that requires modification of C34 in the anticodon loop of isoleucine transfer RNAIleCAU (tRNAIleCAU). Bacterial tRNAIleCAU with 2-lysylcytidine (lysidine) at the wobble position deciphers AUA while avoiding AUG. Here we report cryo-electron microscopy structures of the Escherichia coli 70S ribosome complexed with elongation factor thermo unstable (EF-Tu) and isoleucine-tRNAIleLAU in the process of decoding AUA and AUG. Lysidine in tRNAIleLAU excludes AUG by promoting the formation of an unusual Hoogsteen purine-pyrimidine nucleobase geometry at the third position of the codon, weakening the interactions with the mRNA and destabilizing the EF-Tu ternary complex. Our findings elucidate the molecular mechanism by which tRNAIleLAU specifically decodes AUA over AUG.
The frequency of errors upon decoding of messenger RNA by the bacterial ribosome is low, with one misreading event per 1 × 104 codons. In the universal genetic code, the AUN codon box specifies two amino acids, isoleucine and methionine. In bacteria and archaea, decoding specificity of the AUA and AUG codons relies on the wobble avoidance strategy that requires modification of C34 in the anticodon loop of isoleucine transfer RNAIleCAU (tRNAIleCAU). Bacterial tRNAIleCAU with 2-lysylcytidine (lysidine) at the wobble position deciphers AUA while avoiding AUG. Here we report cryo-electron microscopy structures of the Escherichia coli 70S ribosome complexed with elongation factor thermo unstable (EF-Tu) and isoleucine-tRNAIleLAU in the process of decoding AUA and AUG. Lysidine in tRNAIleLAU excludes AUG by promoting the formation of an unusual Hoogsteen purine-pyrimidine nucleobase geometry at the third position of the codon, weakening the interactions with the mRNA and destabilizing the EF-Tu ternary complex. Our findings elucidate the molecular mechanism by which tRNAIleLAU specifically decodes AUA over AUG.