Abstract
Transfer RNA (tRNA) molecules play vital roles during protein synthesis. Their acceptor arms are aminoacylated with specific amino acid residues while their anticodons delimit codon specificity. The history of these two functions has been generally linked in evolutionary studies of the genetic code. However, these functions could have been differentially recruited as evolutionary signatures were left embedded in tRNA molecules. Here we built phylogenies derived from the sequence and structure of tRNA, we forced taxa into monophyletic groups using constraint analyses, tested competing evolutionary hypotheses, and generated timelines of amino acid charging and codon discovery. Charging of Sec, Tyr, Ser and Leu appeared ancient, while specificities related to Asn, Met, and Arg were derived. The timelines also uncovered an early role of the second and then first codon bases, identified codons for Ala and Pro as the most ancient, and revealed important evolutionary take-overs related to the loss of the long variable arm in tRNA. The lack of correlation between ancestries of amino acid charging and encoding indicated that the separate discoveries of these functions reflected independent histories of recruitment. These histories were probably curbed by co-options and important take-overs during early diversification of the living world.
Highlights
Modern day proteins are synthesized in ribosomes, complex molecular machines made of proteins and RNA
Bootstrap support (BS) values were generally low for most clades, an expected observation given the large number of taxa analyzed
The expansion of amino acids building blocks through evolution has been generally linked to the evolution of the genetic code
Summary
Modern day proteins are synthesized in ribosomes, complex molecular machines made of proteins and RNA. Jordan et al [18] recently revealed a quite different group of early amino acids with declining frequencies in proteins (Ala, Glu, Gly, and Pro) These probabilistic methods and their implicit assumptions were recently questioned [21], and a more stringent approach of only counting fully conserved positions in ribosomal proteins was used to propose that Gln, Gly, Leu, and possibly Pro, Asp, and Asn were encoded earlier, while Cys, Phe, Glu, Ile, Val, Trp, Tyr, and possibly Lys, Glu, and Ser were late additions to the genetic code. It is quite clear that our understanding of how tRNA function has evolved is far from complete
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
