A Scenario on the Stepwise Evolution of the Genetic Code

作     者：Jing-Fa Xiao and Jun Yu CAS Key Laboratory of Genome Sciences and Information,Beijing Institute of Genomics,Chinese Academy of Sciences,Beijing 100029,China. 

出 版 物：《Genomics,Proteomics & Bioinformatics》 (基因组蛋白质组与生物信息学报(英文版))

年 卷 期：2007年第Z1期

页      面：143-151页

核心收录：

学科分类：0710[理学-生物学] 07[理学] 071007[理学-遗传学] 

主　　题：genetic code codon aminoacyl-tRNA synthase GC content 

摘      要：It is believed that in the RNA world the operational (ribozymes) and the infor-mational (riboscripts) RNA molecules were created with only three (adenosine,uridine,and guanosine) and two (adenosine and uridine) nucleosides,respectively,so that the genetic code started uncomplicated. Ribozymes subsequently evolved to be able to cut and paste themselves and riboscripts were acceptive to rigor-ous editing (adenosine to inosine); the intensive diversification of RNA molecules shaped novel cellular machineries that are capable of polymerizing amino acids-a new type of cellular building materials for life. Initially,the genetic code,encoding seven amino acids,was created only to distinguish purine and pyrimidine; it was later expanded in a stepwise way to encode 12,15,and 20 amino acids through the relief of guanine from its roles as operational signals and through the recruitment of cytosine. Therefore,the maturation of the genetic code also coincided with (1) the departure of aminoacyl-tRNA synthetases (AARSs) from the primordial translation machinery,(2) the replacement of informational RNA by DNA,and (3) the co-evolution of AARSs and their cognate tRNAs. This model predicts gradual replacements of RNA-made molecular mechanisms,cellular processes by proteins,and informational exploitation by DNA.