Fig. 7: The structure of the aberrant 50S subunits with 23S-cp5S rRNA.

a Cryo-EM reconstruction of the structure of the 50S subunit in the functional 70S ribosomes (left panel) and unassociated 50S subunit (right panel) containing the 23S-cp5S rRNA. 23S rRNA is light blue, 5S rRNA is red, r-proteins are dark blue. The segments of the PTC rRNA that is remodeled in the aberrant 50S subunit is shown in yellow. b The secondary structure diagram of the central ring of domain V of the 23S rRNA that constitutes the heart of the PTC active site. The rRNA residues misplaced in the aberrant 50S subunits are indicated with red dots. The inlet shows the change in the structure at the H89 base: rearrangement of the PTC structure results in the unwinding of the first helical turn of H89 (see also Supplementary Fig. 5b). c Interaction of the 23S rRNA P-loop (dark blue) with the CCA end of the P-site bound tRNA (green) in the functional ribosome or 23S rRNA segment 2497–2507 (yellow) in the aberrant 23S-cp5S large ribosomal subunits. rRNA strands are colored as in b. In the aberrant 50S subunit, the interaction of the tRNA with P-loop is blocked by the abnormal intramolecular pairing within the 23S rRNA. d Proteins uL16 and bL33 are lacking in the aberrant 50S subunits. Left: the location of uL16 and bL33 (purple) in the large subunit of the active 70S ribosome. 5S rRNA is red. The 23S rRNA segment 2490–2507 in the PTC active site (see b) is shown in yellow. Right: the cryo-EM density for uL16 and bL33 (green mesh) is largely missing in the aberrant 50S subunits.