Abstract:Aminoacyl-tRNA synthetases (aaRSs) are a class of essential enzymes in protein biosynthesis. Study on aaRSs is very important to understand the high fidelity during translation and design new antibiotics. In the present research, leucyl- and arginyl-tRNA synthetases from Escherichia coli have been investigated by cloning, over-expression and site-directed mutagenesis of the genes encoding these enzymes and their cognate tRNAs, in vitro trascription, and recombination of peptide fragments. The results from this research work showed many important points to understand the structure basis of accurate interaction between aaRSs and their cognate tRNAs.