Fig. 6.

rRNA evolution mapped onto the LSU rRNA secondary structure. The common core is built up in six phases, by stepwise addition of ancestral expansion segments at sites marked by insertion fingerprints. (A) Each AES is individually colored and labeled by temporal number. AES colors are arbitrary, chosen to distinguish the expansions, such that no AES is the color of its neighbor. (B) Accretion of ancestral and eukaryotic expansion segments is distributed into eight phases, associated with ribosomal functions. Phase 1, rudimentary binding and catalysis (dark blue); phase 2, maturation of the PTC and exit pore (light blue); phase 3, early tunnel extension (green); phase 4, acquisition of the SSU interface (yellow); phase 5, acquisition of translocation function (orange); phase 6, late tunnel extension (red). Some AESs appear to be discontinuous on the secondary structure and so are labeled twice. A description of each AES and their partitioning into phases is given in SI Appendix, Table S3. The 3D structure of each phase is shown in SI Appendix, Fig. S11.