The sarcin–ricin loop of 23S rRNA is essential for assembly of the functional core of the 50S ribosomal subunit

Disrupted interactions within and between the front and back layers of the ΔSRL-affected region. Protected (orange) and enhanced (blue and pink) nucleotides are shown as in Figure 8; 23S rRNA (gray) helix numbers are indicated. (A) The front layer as seen in the 50S subunit crown view (Fig. 7B). (C) The corresponding back layer, with helix 95 (yellow) and the SRL (red) indicated. B and D are 180° rotations of A and C. (E) Secondary structure of 23S rRNA showing the front (cyan) and back (pink) layers; lines indicate tertiary interactions within the front (blue) or back (magenta) layers or between layers (orange) that are disrupted in the ΔSRL 50S subunits.