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Evolutionary History of the Translational Machinery
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By George Fox & Ashwinikumar Naik

Current theories on the origin of life envision an RNA World as the culmination of chemical evolution. The extent of this RNA World, and the biochemical complexity of the progenotes1 that populated it, is subject to much debate. It, nevertheless, is likely a point of agreement among workers in the field that the discovery of machinery for the chiral synthesis of defined sequence peptides would have paved the way for transition to the modern protein world. With the discovery of an RNA replicase, which might initially have been a catalytic RNA or an early peptide product, the stage would be set for the development of populations of progenotes that had both of these features in one enclosure. Such advanced progenotes would be the first entities capable of having the genetic couple between replication, transcription and translation that is the hallmark of life, as we know it. The modern day tmRNA2 at one stage is recognized as a tRNA by the ribosome while it subsequently serves as a mRNA during translation. This unusual RNA might be representative of the types of entities present in the late RNA World.3 The addition of DNA as a better storage medium for genetic information would finalize the transition from the progenotic world to the living systems that exist in the modern world.

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