The RNA A-helix architects the evolution of the ribosome

The ribosome, biology’s universal translation machinery, marks a significant footprint in the origin of life. Among all rRNA motifs, the RNA A-helix emerges as the most extensive structural element of the ribosome. We hypothesize that the rRNA A-helix motif not only constructs the architectural foundation of the ribosome but also drives its evolution. The large subunit (LSU) ribosome across various species was utilized to study the spatial arrangements of the rRNA A-helices. Remarkably, it exhibits a prevalent spatial distribution of A-helices within the LSU concentrically confined by the bin. These helices are integral to the emergence of peptidyl transferase activity and the preservation of LSU architecture across evolutionary time. The LSU A-helices’ spatial configurations were computationally modeled, allowing us to delineate five evolutionary states of the ancestral LSU. Furthermore, our investigation into the origin of the ancestral mitochondrial LSU suggests an early evolutionary phase characterized by a non-traditional serial endosymbiotic theory (SET), followed by a sequential endosymbiotic theory (EST) event. Our findings underscore the critical role of the rRNA A-helix motif in maintaining the structural integrity of the ribosome and in guiding its evolutionary pathway. These insights provide a new perspective on the fundamental processes underlying the origins of life.