Skip to main content
. 2017 May 24;12(5):e0177972. doi: 10.1371/journal.pone.0177972

Fig 3. Cryo-EM structures of the PoTC.

Fig 3

(A and B) cryo-EM structures reconstructed from images of model PoTC, prepared by treating the purified E. coli endogenous polysomes with Puromycin. (A) The PoTC in unrotated state (EMD-9531) containing one tRNA molecule in P site (green) and mRNA (blue) in the mRNA path. (B) The PoTC in the rotated state (EMD-9530) containing one tRNA molecule in the P/E hybrid state (green) and mRNA (blue) in the mRNA path in the 30S subunit. Segmented densities of all components of the PoTC in this figure are shown at the same contour level. Color code: 50S, aqua; 30S, light brown; tRNA, green; mRNA, blue. Landmarks of ribosome: CP, central protuberance; L1, L1 stalk; St, L7/12 stalk; Sb, L7/12 stalk base; hd, head; bk, beak; pt, platform; sh, shoulder; sp, spur. (C) Fluctuation of tRNA in two different positions in PoTC in conjunction with its configurational rearrangement. Comparison of tRNA positions between two cryo-EM structures obtained from the PoTC specimen. The 30S subunits were used as guides for the precise alignment of the coordinates of the two structures. The anticodon stem loops of the tRNA densities share the same position on 30S subunits, which is the P site. By contrast, the elbow regions and CCA ends of the tRNAs are widely rotated and shifted between the two structures. Cryo-EM structure of mRNA segmented from the rotated PoTC is also shown here. (D) Rotational motion of 30S is shown by the alignment of the 50S portions of two structures from the PoTC specimen. Color code: 50S in rotated state, aqua; 30S in rotated state, light brown; 50S in unrotated state, semitransparent purple; 30S in unrotated state, semitransparent brown. (E) Comparison of tRNA positions in the PoTC with published intermediate positions. Two tRNA positions in the PoTC occur in this study: the P/E hybrid state (green) and classical P-tRNA (orange) are compared with previously reported P/E-tRNAs (PDB ID: 4V9H [20], red; PDB ID: 4V9D [21], purple). (F) P/E-tRNA (green) in the PoTC is compared with tRNA in the Pe*/E intermediate position (PDB ID: 4V9K [22], yellow). (G) P/E-tRNA (green) in the PoTC is compared with tRNA in the Pe/E intermediate position (PDB ID: 4V5N [23], blue).