The article by M. Gouy and C. Gautier explores the correlation between codon usage and gene expressivity in bacteria, particularly focusing on Escherichia coli. They analyze the codon frequencies in 83 sequenced genes from the E. coli genome, including chromosomes, transposons, and plasmids. The study uses two indexes to summarize the codon composition of each gene: one based on the differential usage of iso-tRNA species during translation, and another based on the choice between cytosine (C) and uracil (U) for the third base of codons. The results confirm a strong relationship between codon composition and mRNA expressivity, even for genes within the same operon. The influence of codon usage on peptide elongation rate and protein yield is discussed, and the evolutionary aspects of codon selection in mRNA sequences are also examined. The authors propose that codon usage optimization is driven by strong evolutionary pressures, balancing selection for optimal codons with the mutational process. They suggest that this relationship may be valid for eukaryotic organisms as well, though the optimal codons differ due to differences in anticodon sequences, codon recognition patterns, and iso-tRNA species concentrations.The article by M. Gouy and C. Gautier explores the correlation between codon usage and gene expressivity in bacteria, particularly focusing on Escherichia coli. They analyze the codon frequencies in 83 sequenced genes from the E. coli genome, including chromosomes, transposons, and plasmids. The study uses two indexes to summarize the codon composition of each gene: one based on the differential usage of iso-tRNA species during translation, and another based on the choice between cytosine (C) and uracil (U) for the third base of codons. The results confirm a strong relationship between codon composition and mRNA expressivity, even for genes within the same operon. The influence of codon usage on peptide elongation rate and protein yield is discussed, and the evolutionary aspects of codon selection in mRNA sequences are also examined. The authors propose that codon usage optimization is driven by strong evolutionary pressures, balancing selection for optimal codons with the mutational process. They suggest that this relationship may be valid for eukaryotic organisms as well, though the optimal codons differ due to differences in anticodon sequences, codon recognition patterns, and iso-tRNA species concentrations.