The evolution of aminoacyl-tRNA synthetases: From dawn to LUCA

The origin of all extant life on earth is intimately linked to the establishment of the principal components of the Genetic Code. Aminoacyl-tRNA synthetases (aaRS), by virtue of their universality and essential functions in protein synthesis, count among the biomolecules that evolved to a level of complexity comparable to their extant state before the advent of the Last Universal Common Ancestor (LUCA). Despite the enormous technical difficulties in analyzing such an ancient process, proposals have been put forward to describe the emergence and evolution of the two aaRS families. In this chapter, I critically review some of these proposals and place them along a hypothetical timeline based on other essential aspects of the origin of life. This chapter focuses on the evolution of the aaRS prior to LUCA. Readers will be referred to excellent literature that covers the phylogeny of aaRS in the three extant domains of life.