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♦ See referenced article, J. Biol. Chem. 2013, 288, 26856–26863
The RNA world hypothesis proposes that RNA molecules, which both catalyze some reactions and carry genetic information, evolved before proteins. However, researchers have yet to find ribozymes in living organisms that support this hypothesis. In this Paper of the Week, Charles W. Carter, Jr., and colleagues at the University of North Carolina at Chapel Hill and the University of Vermont argue that peptides and RNA cooperated to develop the genetic code. They demonstrate that Urzymes, which are molecules derived from conserved portions of Class I and Class II aminoacyl-tRNA synthetases, accelerate tRNA aminoacylation by ~106-fold over the uncatalyzed peptide synthesis rate. This excess catalytic proficiency indicates that Urzymes were highly evolved and so probably had even more primitive peptide ancestors. The investigators say that by searching for the evolutionary origins of modern aminoacyl-tRNA synthetases, “we demonstrate key steps for a simpler and hence more probable peptide·RNA development of rapid coding systems matching amino acids with anticodon trinucleotides.” These data have very significant implications for the experimental study of the origin of protein synthesis.