Härtlein M, Cusack S
European Molecular Biology Laboratory, Grenoble Outstation, France.
J Mol Evol. 1995 May;40(5):519-30. doi: 10.1007/BF00166620.
Two aspects of the evolution of aminoacyl-tRNA synthetases are discussed. Firstly, using recent crystal structure information on seryl-tRNA synthetase and its substrate complexes, the coevolution of the mode of recognition between seryl-tRNA synthetase and tRNA(ser) in different organisms is reviewed. Secondly, using sequence alignments and phylogenetic trees, the early evolution of class 2 aminoacyl-tRNA synthetases is traced. Arguments are presented to suggest that synthetases are not the oldest of protein enzymes, but survived as RNA enzymes during the early period of the evolution of protein catalysts. In this view, the relatedness of the current synthetases, as evidenced by the division into two classes with their associated subclasses, reflects the replacement of RNA synthetases by protein synthetases. This process would have been triggered by the acquisition of tRNA 3' end charging activity by early proteins capable of activating small molecules (e.g., amino acids) with ATP. If these arguments are correct, the genetic code was essentially frozen before the protein synthetases that we know today came into existence.
本文讨论了氨酰-tRNA合成酶进化的两个方面。首先，利用最近关于丝氨酰-tRNA合成酶及其底物复合物的晶体结构信息，回顾了不同生物体中丝氨酰-tRNA合成酶与tRNA(ser)识别模式的共同进化。其次，利用序列比对和系统发育树，追溯了2类氨酰-tRNA合成酶的早期进化。有观点认为，合成酶并非最古老的蛋白质酶，而是在蛋白质催化剂进化的早期以RNA酶的形式存活下来。从这个角度来看，目前合成酶的相关性，如分为两类及其相关亚类所证明的，反映了RNA合成酶被蛋白质合成酶所取代。这一过程可能是由早期能够利用ATP激活小分子（如氨基酸）的蛋白质获得tRNA 3'末端充电活性所触发的。如果这些观点正确，那么在我们今天所知道的蛋白质合成酶出现之前，遗传密码基本上就已经固定下来了。
