10 Evolution of Ribosomes and Translation from an RNA World

Abstract

Translation links the nucleotide sequences of genes to the amino acid sequences of proteins, establishing at the molecular level the correspondence between genotype and phenotype. This fundamental process must have arisen early in the history of molecular evolution, before the existence of any genetically encoded protein. To understand how the ribosome and its associated translational ligands, the tRNAs, might have evolved from an RNA World presents one of the most challenging problems to molecular biologists. However, there has been rapid progress in our understanding of the structure and function of ribosomes, and RNA in general, during the past two decades, much of which is represented in this volume. As a consequence, what had once seemed to be a fundamental paradox now presents itself as merely an extraordinarily difficult problem. This chapter summarizes some of the ways in which the new findings have affected this question.

The molecular evolution of translation poses at least three difficult questions: (1) The chicken-or-the-egg problem: if the ribosome requires proteins to function, where did the proteins come from to make the first ribosome? (2) What was the driving force for evolution of the ribosome? and (3) How did coding arise? Thanks to numerous advances in this field, we now have a likely answer to the first question and a plausible basis for answering the second. Despite many decades of thinking about the third question, the origins of coding remain a puzzle. Another question, implicit in the RNA World hypothesis, is (4) Can we account for...