Castresana J, Feldmaier-Fuchs G, Pääbo S
Institute of Zoology, University of Munich, Luisenstrasse 14, D-80333 Munich, Germany.
Proc Natl Acad Sci U S A. 1998 Mar 31;95(7):3703-7. doi: 10.1073/pnas.95.7.3703.
In the mitochondrial genome of the hemichordate Balanoglossus carnosus, the codon AAA, which is assigned to lysine in most metazoans but to asparagine in echinoderms, is absent. Furthermore, the lysine tRNA gene carries an anticodon substitution that renders its gene product unable to decode AAA codons, whereas the asparagine tRNA gene has not changed to encode a tRNA with the ability to recognize AAA codons. Thus, the hemichordate mitochondrial genome can be regarded as an intermediate in the process of reassignment of mitochondrial AAA codons, where most metazoans represent the ancestral situation and the echinoderms the derived situation. This lends support to the codon capture hypothesis. We also show that the reassignment of the AAA codon is associated with a reduction in the relative abundance of lysine residues in mitochondrial proteins.
在半索动物肉形柱头虫的线粒体基因组中，密码子AAA缺失。在大多数后生动物中，该密码子编码赖氨酸，但在棘皮动物中编码天冬酰胺。此外，赖氨酸tRNA基因发生了反密码子替换，使其基因产物无法解码AAA密码子，而天冬酰胺tRNA基因并未改变以编码具有识别AAA密码子能力的tRNA。因此，半索动物线粒体基因组可被视为线粒体AAA密码子重新分配过程中的一个中间阶段，其中大多数后生动物代表原始情况，棘皮动物代表衍生情况。这为密码子捕获假说提供了支持。我们还表明，AAA密码子的重新分配与线粒体蛋白质中赖氨酸残基相对丰度的降低有关。
