On the origin of the genetic code: signatures of its primordial complementarity in tRNAs and aminoacyl-tRNA synthetases

If the table of the genetic code is rearranged to put complementary codons face-to-face, it becomes apparent that the code displays latent mirror symmetry with respect to two sterically different modes of tRNA recognition. These modes involve distinct classes of aminoacyl-tRNA synthetases (aaRSs I a...

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Bibliographic Details
Published in:Heredity 2008-04, Vol.100 (4), p.341-355
Main Authors: Rodin, S N, Rodin, A S
Format: Article
Language:English
Subjects:
Amino acids
Amino Acids - chemistry
Amino Acids - metabolism
Amino Acyl-tRNA Synthetases - metabolism
Anticodon
Base Sequence
Biomedical and Life Sciences
Biomedicine
Codon
Cytogenetics
Ecology
Escherichia coli
Evolution, Molecular
Evolutionary Biology
Genetic Code
Genomics
Human Genetics
Molecular Sequence Data
Plant Genetics and Genomics
review
Ribonucleic acid
RNA
RNA, Transfer - chemistry
RNA, Transfer - genetics
Transfer RNA Aminoacylation
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Summary:If the table of the genetic code is rearranged to put complementary codons face-to-face, it becomes apparent that the code displays latent mirror symmetry with respect to two sterically different modes of tRNA recognition. These modes involve distinct classes of aminoacyl-tRNA synthetases (aaRSs I and II) with recognition from the minor or major groove sides of the acceptor stem, respectively. We analyze the anticodon pairs complementary to the face-to-face codon couplets. Taking into account the invariant nucleotides on either side (5′ and 3′), we consider the risk of anticodon confusion and subsequent erroneous aminoacylation in the ancestral coding system. This logic leads to the conclusion that ribozymic precursors of tRNA synthetases had the same two complementary modes of tRNA aminoacylation. This surprising case of molecular mimicry (1) shows a key potential selective advantage arising from the partitioning of aaRSs into two classes, (2) is consistent with the hypothesis that the two aaRS classes were originally encoded by the complementary strands of the same primordial gene and (3) provides a ‘missing link’ between the classic genetic code, embodied in the anticodon, and the second, or RNA operational, code that is embodied mostly in the acceptor stem and is directly responsible for proper tRNA aminoacylation.
ISSN:0018-067X
1365-2540
DOI:10.1038/sj.hdy.6801086