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. 2022 Dec 22;51(1):449–462. doi: 10.1093/nar/gkac1189

Figure 4.

Figure 4.

Cryo-EM structure of 70S-THR complex with both A- and P-site tRNAs. (A) Overview of the THR binding site (yellow) in the E. coli 70S ribosome containing mRNA (magenta) and full-length Phe-tRNAPhe (green) and tRNAifMet (navy) in the A and P sites, respectively, viewed as a cross-cut section through the ribosome. (B) Close-up view of THR bound in the decoding center in the presence of fully accommodated A-site tRNA. Note that nucleotide C1914 adopts a previously unseen conformation, in which it does not interfere with tRNA binding. (C) Structural re-arrangements in the decoding center (red dashed arrows) upon THR binding and tRNA accommodation. Superpositioning of the previous structure of drug-free ribosome carrying both A- and P-site tRNAs (PDB entry 6XHW (25)) with the two new 70S-THR structures with or without A-site tRNA. The structures were aligned based on helix 44 of the 16S rRNA. Note that in the presence of THR and A-site tRNA, nucleotide C1914 flips halfway out from its normal position in Helix 69 of the 23S rRNA, allowing for tRNA accommodation (light blue to blue transition). However, in the absence of A-site tRNA, nucleotide C1914 is unrestricted and fully flips out (blue to teal transition).