Abstract
BackgroundVertebrate mitochondrial genomes typically have one transfer RNA (tRNA) for each synonymous codon family. This limited anticodon repertoire implies that each tRNA anticodon needs to wobble (establish a non-Watson-Crick base pairing between two nucleotides in RNA molecules) to recognize one or more synonymous codons. Different hypotheses have been proposed to explain the factors that determine the nucleotide composition of wobble sites in vertebrate mitochondrial tRNA anticodons. Until now, the two major postulates – the “codon-anticodon adaptation hypothesis” and the “wobble versatility hypothesis” – have not been formally tested in vertebrate mitochondria because both make the same predictions regarding the composition of anticodon wobble sites. The same is true for the more recent “wobble cost hypothesis”.Principal FindingsIn this study we have analyzed the occurrence of synonymous codons and tRNA anticodon wobble sites in 1553 complete vertebrate mitochondrial genomes, focusing on three fish species with mtDNA codon usage bias reversal (L-strand is GT-rich). These mitogenomes constitute an excellent opportunity to study the evolution of the wobble nucleotide composition of tRNA anticodons because due to the reversal the predictions for the anticodon wobble sites differ between the existing hypotheses. We observed that none of the wobble sites of tRNA anticodons in these unusual mitochondrial genomes coevolved to match the new overall codon usage bias, suggesting that nucleotides at the wobble sites of tRNA anticodons in vertebrate mitochondrial genomes are determined by wobble versatility.Conclusions/SignificanceOur results suggest that, at wobble sites of tRNA anticodons in vertebrate mitogenomes, selection favors the most versatile nucleotide in terms of wobble base-pairing stability and that wobble site composition is not influenced by codon usage. These results are in agreement with the “wobble versatility hypothesis”.
Highlights
Twelve of all 13 protein-coding genes encoded on the vertebrate mitogenomes are collinear with the AC-rich lightstrand, while ND6 is the only protein-coding gene located in the opposite strand [1]
Conclusions/Significance: Our results suggest that, at wobble sites of transfer RNA (tRNA) anticodons in vertebrate mitogenomes, selection favors the most versatile nucleotide in terms of wobble base-pairing stability and that wobble site composition is not influenced by codon usage
This fact implies that each tRNA anticodon must wobble with one or more nucleotides to recognize all codons in a synonymous codon family [3]
Summary
Twelve of all 13 protein-coding genes encoded on the vertebrate mitogenomes are collinear with the AC-rich lightstrand, while ND6 is the only protein-coding gene located in the opposite strand (heavy-strand) [1]. A codon family consists of all synonymous codons, which differ only in their third codon position but code the same amino acid This fact implies that each tRNA anticodon must wobble with one or more nucleotides to recognize all codons in a synonymous codon family [3]. Vertebrate mitochondrial genomes typically have one transfer RNA (tRNA) for each synonymous codon family. This limited anticodon repertoire implies that each tRNA anticodon needs to wobble (establish a non-Watson-Crick base pairing between two nucleotides in RNA molecules) to recognize one or more synonymous codons. Different hypotheses have been proposed to explain the factors that determine the nucleotide composition of wobble sites in vertebrate mitochondrial tRNA anticodons. The same is true for the more recent ‘‘wobble cost hypothesis’’
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