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. Author manuscript; available in PMC: 2014 Dec 1.
Published in final edited form as: Biopolymers. 2013 Dec;99(12):1147–1166. doi: 10.1002/bip.22293

Figure 1.

Figure 1

Overall architecture of the 70S bacterial ribosome, in its classical, unrotated state (PDB: 3I8G,36 3I8F,36 2WRJ37) (A) The 70S bacterial ribosome is made of two subunits, 30S (blue, also in B) and 50S (brown, also in C). The two subunits stack together with their A- (aminoacyl), P- (peptidyl), and E- (exit) sites facing inward toward each other, thus defining an intersubunit interface where cycles of translation occur. Ribosomal proteins are shown as ribbons; ribosomal RNAs are lighter color, and the mRNA is space filling in red. The tRNAs are violet for A-, green for P-, and yellow for E-tRNA; the same color-coding for these classical state tRNAs is used in all figures. Ribosomal proteins L1 and L9 are identified on the left side of the 50S subunit (L designates proteins from the 50S subunit, S from the 30S). The decoded mRNA lies between the 30S head and body domains, wrapped in an inverted U-shape around the 30S neck (shown in panel B). (B) 30S, view from the mRNA entrance (3'-end shown) with the 50S removed. A trench-like region on the 30S is its neck, which serves as a saddle to display the decoded mRNA (red) codons. The appropriate interactions between the anticodon stem-loop of the tRNAs and the decoded codons on the mRNA are probed by highly conserved resides (detailed in Figure 4), which are adjacent to the neck and come both sides from the 30S head and body. The L-shape tRNAs have their aminoacyl-acceptor ends oriented toward the upper-right corner, revealing how their corresponding binding-sites on the 50S are configured parallel in space. (C) 50S, view of its tRNA-binding/intersubunit interface. The codon-anticodon duplex (red) is out from the paper plane toward us, whereas the aminoacyl-acceptor ends of the tRNAs are bound tightly within each of their designated cavities, clustering around the center of the 50S. Note that the A- and PtRNA acceptorends are positioned relatively close to each other and to the nearby peptidyl-transferase center (PTC). This is where elongations of the polypeptide chain take place.