Extended Data Figure 4.

Bacterial ribosomes contain about 55 r-proteins (blue) that average ~130 amino acids and make up 30–35% of the ribosome mass. Eukaryotic ribosomes contain about 80 r-proteins that average ~165 amino acids and make up about 45% of the ribosome mass. In both these cases ribosomes catalyse their own production. In contrast, in mitochondrial ribosomes which do not produce themselves rRNA (gray) is scarcer, and r-proteins are significantly larger and could make up as much as 80% of the ribosome mass.