Supplemental Data 1. Example of the electron density map (contoured at 1.5 σ) showing the quality of the experimental data. The close-up view displays a detail of the interface between the two subunits made by residues of the CP1 domains.

Supplemental Data 2. Cα–Cα distances calculated after least squares minimized superimposition of two subunits of mt-TyrRS-ΔS4 in complex with Tyr-AMS. The red line indicates the overall r.m.s.d. Crystallographic contacts for each monomer (orange for monomer A, red for monomer B) are indicated by dots above the graphic (full dots for contacts < 3.2 Å; empty dots for contacts in the 3.2–4.0 Å range). To facilitate data interpretation, the figure recalls the modular organization of the TyrRS (color code as in Figure 1A) with structural details (as in Figure 1B).

Supplemental Data 3. Sequence alignment of 40 mitochondrial TyrRSs with conserved, semi-conserved, and strategic residues indicated (see legend of Figure 1B). The alignment highlights in particular the critical domains (H0, ins1, HIGH, ins2, cluster 1, cluster 2 and KMSKS) discussed in the main text. Sequences were extracted from various databases, annotated (human, mouse, drosophila, yeast, N. crassa), predicted or manually rebuilt. For these two latter categories, identification was validated by the presence of a mitochondrial targeting sequence and multiple sequence alignments.