Woese C R, Olsen G J, Ibba M, Söll D
Department of Microbiology, University of Illinois, Urbana, Illinois 61801, USA.
Microbiol Mol Biol Rev. 2000 Mar;64(1):202-36. doi: 10.1128/MMBR.64.1.202-236.2000.
The aminoacyl-tRNA synthetases (AARSs) and their relationship to the genetic code are examined from the evolutionary perspective. Despite a loose correlation between codon assignments and AARS evolutionary relationships, the code is far too highly structured to have been ordered merely through the evolutionary wanderings of these enzymes. Nevertheless, the AARSs are very informative about the evolutionary process. Examination of the phylogenetic trees for each of the AARSs reveals the following. (i) Their evolutionary relationships mostly conform to established organismal phylogeny: a strong distinction exists between bacterial- and archaeal-type AARSs. (ii) Although the evolutionary profiles of the individual AARSs might be expected to be similar in general respects, they are not. It is argued that these differences in profiles reflect the stages in the evolutionary process when the taxonomic distributions of the individual AARSs became fixed, not the nature of the individual enzymes. (iii) Horizontal transfer of AARS genes between Bacteria and Archaea is asymmetric: transfer of archaeal AARSs to the Bacteria is more prevalent than the reverse, which is seen only for the "gemini group. " (iv) The most far-ranging transfers of AARS genes have tended to occur in the distant evolutionary past, before or during formation of the primary organismal domains. These findings are also used to refine the theory that at the evolutionary stage represented by the root of the universal phylogenetic tree, cells were far more primitive than their modern counterparts and thus exchanged genetic material in far less restricted ways, in effect evolving in a communal sense.
从进化的角度研究了氨酰 - tRNA合成酶（AARSs）及其与遗传密码的关系。尽管密码子分配与AARS进化关系之间存在松散的相关性，但遗传密码的结构过于高度有序，不可能仅仅通过这些酶的进化演变来排序。然而，AARSs对于进化过程具有重要的信息价值。对每种AARSs的系统发育树进行研究可得出以下结论。（i）它们的进化关系大多符合已确立的生物系统发育：细菌型和古细菌型AARSs之间存在明显区别。（ii）尽管单个AARSs的进化概况在一般方面可能预期相似，但实际并非如此。有人认为，这些概况上的差异反映了进化过程中各个AARSs的分类分布固定下来的阶段，而非单个酶的性质。（iii）细菌和古细菌之间AARS基因的水平转移是不对称的：古细菌AARSs向细菌的转移比相反方向更普遍，相反方向仅在“双子组”中可见。（iv）AARS基因最广泛的转移往往发生在遥远的进化过去，即在主要生物域形成之前或期间。这些发现也被用于完善这样一种理论，即在以通用系统发育树根部为代表的进化阶段，细胞比现代细胞原始得多，因此以限制少得多的方式交换遗传物质，实际上是以群体方式进化。
