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<p>Frameshifts can be caused by specific combinations of tRNA and mRNA. The wildtype AGC-decoding <i>E. coli</i> tRNA<sup>Ser3</sup><sub>GCU</sub> has been shown to induce −1 ribosomal frameshifting on GCA alanine codons, and proposed to read a two-base codon instead of a canonical triplet. However, it has remained unclear whether this type of non-cognate decoding can be accommodated by the ribosome. Here, we perform single-particle cryo-EM reconstructions on <i>E. coli</i> 70S ribosomes with the frameshift-inducing tRNA<sup>Ser3</sup> bound to the non-cognate GCA codon or the cognate AGC codon in the ribosomal A site. The structures demonstrate that doublet&#xa0;decoding is made possible when A1493, the conserved monitoring base in 16S rRNA, mimics a first codon base, forming a Hoogsteen base pair with U36 from the anticodon and stacking with the mRNA. This interaction pushes the first two bases of the A-site codon in position for base pairing with C35 and G34 of the anticodon.</p>

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Doublet decoding of tRNASer3 demonstrates plasticity of ribosomal decoding center

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年6月26日

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  • Shruthi Krishnaswamy,
  • Shirin Akbar,
  • Daniel S. D. Larsson,
  • Yang Chen,
  • Maria Selmer

摘要

Frameshifts can be caused by specific combinations of tRNA and mRNA. The wildtype AGC-decoding E. coli tRNASer3GCU has been shown to induce −1 ribosomal frameshifting on GCA alanine codons, and proposed to read a two-base codon instead of a canonical triplet. However, it has remained unclear whether this type of non-cognate decoding can be accommodated by the ribosome. Here, we perform single-particle cryo-EM reconstructions on E. coli 70S ribosomes with the frameshift-inducing tRNASer3 bound to the non-cognate GCA codon or the cognate AGC codon in the ribosomal A site. The structures demonstrate that doublet decoding is made possible when A1493, the conserved monitoring base in 16S rRNA, mimics a first codon base, forming a Hoogsteen base pair with U36 from the anticodon and stacking with the mRNA. This interaction pushes the first two bases of the A-site codon in position for base pairing with C35 and G34 of the anticodon.