Origins and early evolution of the ribosome

Abstract

The modern ribosomal machinery is very complex, and its core subsystems and many of its individual components are universally found in all three domains of life. This indicates that much of the story of ribosome origins and its subsequent evolution predates the last universal common ancestor (LUCA). Thus, ribosome history relates to other early life issues such as the possibility and nature of an RNA World, the early history of chirality, and always most hopefully the origins of the genetic code. However, this is not the end of the story. As discussed elsewhere in this volume, important events have also occurred since the LUCA, especially in eukaryotic ribosomes that have served to integrate the machinery with other cellular systems. Ribosome origins and subsequent evolution are in reality somewhat separate problems. In addressing the former, this chapter initially examines the source and nature of the peptidyl transferase center (PTC), including where and how the peptide bond is made. This is followed by efforts to understand the subsequent evolution of the ribosome, which led to the addition and refinement of various other functional centers including the decoding center. This is being accomplished using what is in essence a reverse engineering approach to develop a timeline of major events in the ribosome history. Finally, significant events on the timeline are discussed in detail.