Extended Data Figure 7: The E-site and the P-site finger of the 39S subunit.
From: The complete structure of the large subunit of the mammalian mitochondrial ribosome
a, 39S subunit (16S rRNA, orange; ribosomal proteins, cyan; uL28m, purple; uL33m, green) with E-site tRNA (blue) modelled based on the superposition of the structure of the bacterial ribosome with bound tRNAs15. The residues corresponding to the tRNA 3′ end binding pocket in bacteria15 are shown in dark red. b, In bacterial ribosomes (23S rRNA, grey; ribosomal proteins, light brown; L1 stalk omitted for clarity, otherwise as in a), rRNA helix 68 (yellow) additionally interacts with the E-site tRNA. This structural element is missing in the 39S subunit. c, The pocket into which the terminal nucleotide of the E-site tRNA inserts in bacterial 23S rRNA (grey)26 is conserved in the mitochondrial 16S rRNA (orange). Ribosomal protein uL28 (light brown) interacts with the E-site tRNA in bacteria15, but is shortened in the 39S subunit (uL28m in purple). d, mL40 (yellow), mL64 (CRIF1, MRPL59) (green) and mL48 (red) approach the area where the E- and P-site tRNAs are located based on superposition of the bacterial structure15. 16S rRNA in orange, 39S proteins in pale cyan. e, Cryo-EM density of the 55S mitoribosome (filtered to 6 Å resolution) segmented into 39S and 28S subunits and A- and P-site tRNAs. The P-site finger is inserted between the A- and P-site tRNAs and contacts both tRNAs. f, Same as e, but shown in top view with part of the ribosome segmented away to reveal the tRNAs.
