Fig. 6: mt-LSU and mt-SSU assembly intermediates accumulate in GTPBP8 knock-out cells.

A Upper panel. The mature secondary structure of the 16 S mt-rRNA is represented and the disordered helices of each mt-LSU sub-assembly state in GTPBP8 knock-out cells are highlighted in yellow. The gray box indicates the presence of helices H80-81, H65, and 1709-1736 nt in State 2 as compared to State 1. Lower panel. Cryo-EM densities are shown for each assembly state (State 1 and 2) and the proportion of each population is indicated as a percentage. The model-based surface of bL36m is shown in dashed lines and transparent color in both assembly states where it is lacking (PDB: 5OOL⁴²). A comparison of each state with the mature mt-LSU (EMD:2762) highlights the regions of 16 S mt-rRNA which are disordered under GTPBP8 depletion (yellow). In the right panel, 16 S mt-rRNA modifications are indicated. The densities were Gaussian filtered in ChimeraX for easier visualization. B Cryo-EM densities of mt-SSU populations are shown for each state and the proportion of each population is indicated as a percentage. Model-based surfaces of mS37 are shown in dashed lines and transparent color in the states where it is lacking. Density maps are highlighted in color in the states where METTL15, mS37, mtIF3, mtIF2, and fMet-tRNA^Met are present (PDB: 6RW5⁴⁴). For each state, zoomed-in panels of mS37, METTL15, mtIF3, mtIF2, and fMet-tRNA^Met maps and models are represented (PDB: 6RW5⁴⁴; 7PNX⁴⁰). The red circle highlights the unassigned density close to the mtIF3 C-terminal domain in State 3. The black squares at the tip of the mt-SSU tail in States 2, 3, and 4 highlight the unassigned extra density in proximity of mS27::FLAG. In State 1, the absence of this extra density is shown as a dashed shape. The densities were Gaussian filtered in ChimeraX for easier visualization.