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Life 2016, 6(1), 10; doi:10.3390/life6010010

Clues to tRNA Evolution from the Distribution of Class II tRNAs and Serine Codons in the Genetic Code

Department of Biochemistry, University of Otago, Dunedin 9016, New Zealand
Academic Editors: Lluís Ribas de Pouplana, Adrian Gabriel Torres and Helga Stan-Lotter
Received: 1 December 2015 / Revised: 20 February 2016 / Accepted: 22 February 2016 / Published: 24 February 2016
(This article belongs to the Special Issue Evolution of tRNA)
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Abstract

We have previously proposed that tRNAGly was the first tRNA and glycine was the first amino acid incorporated into the genetic code. The next two amino acids incorporated would have been the other two small hydrophilic amino acids serine and aspartic acid, which occurred through the duplication of the tRNAGly sequence, followed by mutation of its anticodon by single C to U transition mutations, possibly through spontaneous deamination. Interestingly, however, tRNASer has a different structure than most other tRNAs, possessing a long variable arm; because of this tRNASer is classified as a class II tRNA. Also, serine codons are found not only in the bottom right-hand corner of the genetic code table next to those for glycine and aspartic acid, but also in the top row of the table, next to those for two of the most hydrophobic amino acids, leucine and phenylalanine. In the following, I propose that the class II tRNA structure of tRNASer and the arrangement of serine codons in the genetic code provide clues to the early evolution of tRNA and the genetic code. In addition, I address Di Giulio’s recent criticism of our proposal that tRNAGly was the first tRNA, and discuss how early peptides produced from a restricted amino acid alphabet of glycine, serine and aspartic acid might have possessed proteolytic activity, which is possibly important for the early recycling of amino acid monomers. View Full-Text
Keywords: transfer RNA; tRNA evolution; genetic code; small hydrophilic amino acids; class II tRNAs; tRNA introns; aspartic protease; recycling transfer RNA; tRNA evolution; genetic code; small hydrophilic amino acids; class II tRNAs; tRNA introns; aspartic protease; recycling
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Bernhardt, H.S. Clues to tRNA Evolution from the Distribution of Class II tRNAs and Serine Codons in the Genetic Code. Life 2016, 6, 10.

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