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Codon reassignment and amino acid composition in hemichordate mitochondria
J Castresana1, G Feldmaier-Fuchs, S Pääbo
1Institute of Zoology, University of Munich, Luisenstrasse 14, D-80333 Munich, Germany. castresa@zi.biologie.uni-muenchen.de
Summary
The hemichordate mitochondrial genome is missing the AAA codon, supporting the codon capture hypothesis. This genetic intermediate shows a shift in amino acid assignment, with fewer lysine residues in proteins.
Area of Science:
- Mitochondrial genomics
- Evolutionary biology
- Molecular genetics
Background:
- The AAA codon is typically assigned to lysine in most animals but to asparagine in echinoderms.
- Hemichordates represent a crucial evolutionary link between deuterostome groups.
Purpose of the Study:
- To investigate the status of the AAA codon in the hemichordate mitochondrial genome.
- To understand the evolutionary trajectory of codon reassignment in mitochondrial DNA.
- To examine the relationship between codon usage and protein composition.
Main Methods:
- Bioinformatic analysis of the Balanoglossus carnosus mitochondrial genome.
- Comparative genomics of tRNA genes and codon usage patterns.
- Analysis of amino acid composition in mitochondrial proteins.
Main Results:
- The AAA codon is absent in the Balanoglossus carnosus mitochondrial genome.
- The lysine tRNA gene shows an anticodon modification preventing AAA codon recognition.
- The reassignment of the AAA codon correlates with a decreased abundance of lysine in mitochondrial proteins.
Conclusions:
- The hemichordate mitochondrial genome represents an intermediate state in AAA codon reassignment, supporting the codon capture hypothesis.
- This finding clarifies the evolutionary pathway from ancestral to derived codon usage in metazoan mitochondria.
- Changes in codon usage directly impact the amino acid composition of mitochondrial proteins.