Fig. 1: High-resolution structures of four consecutive trans-translation states.
From: Structures of tmRNA and SmpB as they transit through the ribosome
Shown are the a pre-accommodation (PRE-ACC), b accommodation (ACC), c translocation (TRANS) and d intermediate post-translocation (TRANS*) complexes. Top, schematic representations of the complexes showing the ribosomal 50S (blue) and 30S (khaki) subunits, non-stop mRNA (yellow), P-site tRNAphe (green), elongation factor EF-Tu (pink), SmpB (purple) and tmRNA (red). Also indicated are the ribosome’s A, P and E sites, and the tmRNA structural domains: the H2 helix, H5 stem-loop, pseudoknot (PK) ring, mRNA-like domain (MLD) and tRNA-like domain (TLD). Middle, electron density maps contoured at 2.5 σ, where sigma refers to the variance in the map. Bottom, the same density maps rotated by 180° around the Y-axis and 45° around the X-axis. e–h Cross-sections of the 30S subunits in the same states as (a–d), respectively, showing the SmpB C-terminal tail, non-stop mRNA and the MLD in the mRNA channel.
