Cross evolutionary profiling of ribosomal modifications from nucleobase to near atomic resolution

Protein translation in the cell is conducted by ribosomes, robust cellular organelles composed of a highly conserved catalytic RNA core and dozens of auxiliary proteins. Among the highly evolutionarily conserved - yet poorly understood - features of the ribosome is its susceptibility to post-transcriptional modifications. For many years, the ribosome was regarded as a homogenous multi-component organelle. As such, it was also tacitly assumed that rRNA modifications formed a constitutive part of the ribosome. However, advances in recent years have challenged this assumption, as it is becoming increasingly clear that different pools of ribosomes exist within cells. Such heterogeneity is increasingly believed to have functional consequences both under physiological conditions, and disease - albeit direct proof for such mechanism is yet to be provided. Using a combination of genetic and structural approaches we have recently shown that rRNA modifications in thermophilic archaea immerge at unprecedented levels and are dramatically induced in response to temperature. This work conjugated to phenotype studies in strains deficient in enzymes responsible for installing these modifications exhibit temperature-dependent growth defects, thus implicated their potential role in rRNA thermostability. Our structural work included the delineation of near-atomic resolution structures of WT and modification depleted strains by cryo-EM determined at 2.6-2.9 Å resolutions. These structures furnished structural insights into the temperature-dependent distribution of this modification and its potential thermoadaptive role, providing for the first time direct evidence for the role and phenomena of tunable ribosome modifications in adaptation to external environmental conditions.