Andersson G E, Kurland C G
Department of Molecular Biology, Uppsala University, Sweden.
Mol Biol Evol. 1991 Jul;8(4):530-44. doi: 10.1093/oxfordjournals.molbev.a040666.
We argue that in animal mitochondria codon reassignments, such as those for AGA and AGG from arginine to serine or of AUA from isoleucine to methionine, are the result of an interplay between biased mutational forces and selective ones. In particular, there is a marked tendency for animal mitochondria to have very small genomes and to minimize their investment in components required for gene expression. These tendencies are expressed as a reduction in the diversity of tRNA isoacceptor species. In our view, the pressure to simplify tRNA populations, together with mutational bias against certain codons, will account for the codon reassignments observed in animal mitochondria. A parallel to the major codon bias in microorganisms, which likewise tends to reduce the diversity of the tRNA isoacceptor populations under fast growth conditions, may be drawn. Therefore, we suggest that codon reassignments are usefully viewed as an extreme form of codon bias.
我们认为，在动物线粒体中密码子重新分配现象，例如精氨酸的AGA和AGG密码子重新分配为丝氨酸密码子，或者异亮氨酸的AUA密码子重新分配为甲硫氨酸密码子，是偏向性突变力量和选择性力量相互作用的结果。具体而言，动物线粒体具有显著的倾向，即拥有非常小的基因组，并尽量减少其在基因表达所需组件上的投入。这些倾向表现为tRNA同工受体种类多样性的降低。我们认为，简化tRNA群体的压力，以及对某些密码子的突变偏向性，将解释在动物线粒体中观察到的密码子重新分配现象。可以将其与微生物中的主要密码子偏向性进行类比，在快速生长条件下，微生物的密码子偏向性同样倾向于减少tRNA同工受体群体的多样性。因此，我们建议将密码子重新分配有效地视为密码子偏向性的一种极端形式。
