Primary Citation of Related Structures: 9GXX, 9H0L
PubMed Abstract:
Frameshifts can be caused by specific combinations of tRNA and mRNA. The wildtype AGC-decoding E. coli tRNA Ser3 GCU 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 tRNA Ser3 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.
Organizational Affiliation:
Department of Cell and Molecular Biology, Uppsala University, BMC, P.O. Box 596, SE-75124, Uppsala, Sweden.
Department of Integrated Structural Biology, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), 67400, Illkirch, France.
MAX IV Laboratory, Lund University, P.O. Box 118, SE-221 00, Lund, Sweden.
Department of Cell and Molecular Biology, Uppsala University, BMC, P.O. Box 596, SE-75124, Uppsala, Sweden. maria.selmer@icm.uu.se.
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