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. 2014 Mar 21;5:113. doi: 10.3389/fmicb.2014.00113

Figure 8.

Figure 8

Cryo-EM maps of the currently-solved trans-translation functional complexes. Non-productive translation complex (NTC): the ribosome stalls at the 3′-end of the mRNA, the A-site lacks a complete codon. Pre-accommodation: The alanyl-tmRNA•SmpB•EF-Tu•GTP quaternary complex enters the vacant A-site of a non-stop stalled ribosome (EMDB entry: EMD-1312) (Valle et al., 2003; Kaur et al., 2006). Accommodation: EF-Tu dissociates after GTP hydrolysis, allowing tmRNA-SmpB to occupy the A-site (EMDB entry: EMD-5188) (Weis et al., 2010a). Translocation: EF-G•GTP catalyzes the translocation of tmRNA-SmpB to the P-site. The ribosome is in a ratcheted state and a unique swivel of the head is observed (EMDB entry: EMD-5386) (Ramrath et al., 2012). Post-translocation: After dissociation of EF-G•GDP, the subunits return to normal positioning, and the resume codon of tmRNA is correctly placed into the A-site (EMDB entry: EMD-5189) (Weis et al., 2010a). Re-registration: Translation switches on the tmRNA internal ORF, and a new aminoacyl-tRNA binds to the resume codon (EMDB entry: EMD-5234) (Fu et al., 2010). Color code: the large 50S subunit is light blue; the small 30S subunit is pale yellow; the truncated mRNA is yellow; the nascent polypeptide is teal; the tRNA initially occupying the E-site is orange; the tRNA initially occupying the P-site is green; the tmRNA is red; the SmpB is magenta; the EF-Tu is light pink; the EF-G is blue; and the A site-tRNA is purple.