Pan-modification profiling facilitates a cross-evolutionary dissection of the thermoregulated ribosomal epitranscriptome.

Ribosomal RNA (rRNA) constitutes the core of ribosomes and is extensively chemically modified. Technical challenges have precluded systematically dissecting rRNA modifications and their dynamics. We develop Pan-Mod-seq, permitting inference of 16 distinct modifications across dozens of samples in parallel. We applied Pan-Mod-seq to RNA from 14 species spanning all domains of life, cultured under highly diverse conditions. While dynamic modifications are rare in mesophiles, in extreme hyperthermophiles, ∼50% of modifications are dynamic. We dissect the biogenesis and function of a conserved module of tandem m⁵C-ac⁴C modifications, co-induced at high temperatures, via enzymes intrinsically regulated by temperature and required for growth at higher temperatures. Cryo-electron microscopy (cryo-EM) structures of ribosomes from wild-type (WT) and enzyme-deficient archaea reveal recurrent molecular interactions through which they confer structural stability, and biophysical studies demonstrate their synergistic thermostabilizing role. Our findings systematically dissect rRNA modification plasticity and pave the way for surveying the rRNA epitranscriptome in health and disease.