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On the Origin of Translation and Ribosomes

The emergence of coupling between two polymers of life – nucleic acids and proteins – was a key step in the transition from inanimate to animate matter on earth. It facilitated the translation of linear genetic polymers into information stored in three-dimensional structures, capable of performing a wide variety of functions that we associate with living systems. Despite recent progress in understanding the structure and mechanism of action of the ribosome, the central unit mediating translation of RNA to proteins, the earliest history of coupling between these polymers remains both enigmatic and controversial. Below are three contributions that provide an excellent summary of recent efforts aimed at unraveling the mystery associated with the origin of translation. Michael Yarus addresses the early origins of the genetic code. He briefly reviews a hypothesis that recognition between amino acids and RNA template was driven by stereochemical fit and discusses supporting experimental evidence. According to this hypothesis, specific RNA binding sites were selected because they represented the simplest coding system. Loren Williams presents an evolutionary “onion” model of the ribosome that has at its innermost core the peptidyl transferase center (PTC), a rather non-specific catalytic center that might have been capable of carrying out multiple functions ...

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A genetic code from RNA chemistry: binding sites for amino acids and peptides

Written by: Michael Yarus (Michael.Yarus@colorado.edu); Department of Molecular, Cellular, and Developmental Biology, University of Colorado Boulder; Boulder, CO, USA

Edited by: Aaron Engelhart and Andrew Pohorille

The genetic code is a set of associations, linking the twenty-some common amino acids and the 64 triplet sequences of four nucleotides. These connections are almost universally conserved among life on Earth. The same code, with only small and temporary variations, has apparently been used by every terran organism since before their last universal common ancestor (LUCA). Accordingly, there is a large literature musing, speculating, or guessing about the code’s unanimous acceptance by the only biota known on our planet. This short review, however, takes a different tack, suggesting that there is an experimental, currently demonstrable, chemical connection between (some) amino acids and (some) encoding nucleotides.

A molecular fossil? The story begins 23 years ago, with the elucidation of the active site of the Tetrahymena group I self-splicing RNA. The group I intron binds a guanosine or G nucleotide cofactor at a specific site to initiate its RNA splicing sequence. Within the same binding site, arginine can also be bound (1). Strikingly, there are conserved codons (CGA and AGA) for ...

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