After decoding at the aminoacyl (A) site, the crystal structure of the anticodon stem-loop of tRNA SufA6 bound in the more » peptidyl (P) site reveals ASL conformational changes that allow for recoding into the +1 mRNA frame. Here, we determined the structural basis for how frameshift-suppressor tRNA SufA6 (a derivative of tRNA Pro ) reprograms the mRNA frame to translate a 4-nt codon when bound to the bacterial ribosome. Certain tRNAs can cause a shift out of frame (i.e., frameshifting) due to imbalances in tRNA concentrations, lack of tRNA modifications or insertions or deletions in tRNAs (called frameshift suppressors). « lessĪccurate translation of the genetic code is critical to ensure expression of proteins with correct amino acid sequences. In conclusion, our results reveal how the tRNA modification at nucleotide 37 stabilizes interactions with the mRNA codon to preserve the mRNA frame. Further, an X-ray crystal structure of the 70S ribosome bound to tRNA SufA6 U32♺37.5 at 3.6 Å resolution shows a reordering of the anticodon loop consistent with the findings from the high-affinity measurements. Restoring the tRNA SufA6 U32♺37.5 pairing results in a high-affinity association on the slippery CCC-U codon. One reason for this destabilization is the disruption of a conserved U32♺38 nucleotide pairing in the anticodon stem through insertion of G37.5. In this work, we solved structures of the bacterial ribosome containing either wild-type tRNA$$^$$ derivative containing an extra nucleotide in its anticodon loop that undergoes +1 frameshifting, reveal that m 1G37 destabilizes interactions with both the cognate CCG and slippery codons. The molecular basis for how these two tRNA features combine to ensure accurate decoding is unclear. Disruption of this correlation renders the ribosome unable to distinguish correct from incorrect tRNAs. In the tRNA anticodon stem-loop, the anticodon sequence is correlated with a base pair in the anticodon loop (nucleotides 32 and 38) to tune the binding of each tRNA to the decoding center in the ribosome. Bacterial transfer RNAs (tRNAs) contain evolutionarily conserved sequences and modifications that ensure uniform binding to the ribosome and optimal translational accuracy despite differences in their aminoacyl attachments and anticodon nucleotide sequences.
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