Fig. 3: Structural comparison of assembly intermediates.

a Table of six described assembly intermediates each compromising at least one of the assembly factors MTG3, TFB1M, or mtRBFA, as well as the mature mtSSU (PDB: 3J9M²;). Maturation of 12S rRNA modules is shown for each state (matured: “+”, unmatured: “−”). b The previously described assembly state (PDB 8CSP²⁰) (left) as well as state A (this study) (right) are shown side-by-side, with additional modules highlighted (right). The 12S rRNA and indicated biogenesis factors are shown as cartoon and the remaining mitoribosomal proteins (MRPs) are indicated as white transparent surface. Depiction as follows (state A vs PDB 8CSP²⁰): 12S rRNA: red vs peach, MTG3: light blue vs dark blue, TFB1M: lime green vs dark green, mtRBFA: indigo, bS21m, uS21m, uS15m: beige, METTL17: yellow, MCAT: light blue, ERAL1: dark purple. c Zoomed-in view of h18 and TFB1M in state A d Zoomed-in view of MTG3 (light blue) and uS15m (beige) in state A vs additional ordered regions of MTG3 in a previous state (PDB 8CSP²⁰) (c, d) Densities from map A3 (c) and A2 (d) are depicted as transparent surfaces. e Side-by-side view of state B (right) and C (left) with coloring as followed: 12S rRNA: red vs peach, METTL15: dark vs light turquoise, mtRBFA: indigo vs dark violet. f Different routes of the rRNA content in state B vs state C. The model of state C is shown superimposed to the model of state B, with 12S rRNA density from state B (map B3) depicted transparent. g Close-up view of METTL15-mtRBFA⁽ⁱⁿ⁾ interaction in state B superimposed with METTL15 from state C and depicted mito-specific extension from of METTL15. The 12S rRNA and MRPs are indicated as transparent surface.