Department of Biological Sciences, Bowling Green State University, Bowling Green, OH, United States.
J Theor Biol. 2019 Apr 7;466:1-10. doi: 10.1016/j.jtbi.2019.01.022. Epub 2019 Jan 15.
The genetic code, as arranged in the standard tabular form, displays a non-random structure relating to the characteristics of the amino acids. An alternative arrangement can be made by organizing the code according to aminoacyl-tRNA synthetases (aaRSs), codons, and reverse complement codons, which illuminates a coevolutionary process that led to the contemporary genetic code. As amino acids were added to the genetic code, they were recognized by aaRSs that interact with stereochemically similar amino acids. Single nucleotide changes in the codons and anticodons were favored over more extensive changes, such that there was a logical stepwise progression in the evolution of the genetic code. The model presented traces the evolution of the genetic code accounting for these steps. Amino acid frequencies in ancient proteins and the preponderance of GNN codons in mRNAs for ancient proteins indicate that the genetic code began with alanine, aspartate, glutamate, glycine, and valine, with alanine being in the highest proportions. In addition to being consistent in terms of conservative changes in codon nucleotides, the model also is consistent with respect to aaRS classes, aaRS attachment to the tRNA, amino acid stereochemistry, and to a large extent with amino acid physicochemistry, and biochemical pathways.
遗传密码以标准表格形式排列，显示出与氨基酸特性相关的非随机结构。通过根据氨酰-tRNA 合成酶 (aaRS)、密码子和反向互补密码子来组织密码子，可以进行另一种排列，这揭示了导致当代遗传密码的共同进化过程。随着氨基酸被添加到遗传密码中，它们被与立体化学上相似的氨基酸相互作用的 aaRS 识别。与更广泛的变化相比，密码子和反密码子中的单个核苷酸变化更受青睐，因此遗传密码的进化有一个合乎逻辑的逐步进展。所提出的模型追踪了遗传密码的进化，考虑了这些步骤。古代蛋白质中的氨基酸频率和古代蛋白质的 mRNA 中 GNN 密码子的优势表明，遗传密码从丙氨酸、天冬氨酸、谷氨酸、甘氨酸和缬氨酸开始，其中丙氨酸的比例最高。除了在密码子核苷酸的保守变化方面一致外，该模型还与 aaRS 类、aaRS 与 tRNA 的结合、氨基酸立体化学以及在很大程度上与氨基酸物理化学和生化途径一致。
