Preference for guanosine at first codon position in highly expressed Escherichia coli genes. A relationship with translational efficiency

Abstract

The variation in base composition at the three codon sites in relation to gene expressivity, the latter esti- mated by the Codon Adaptation Index, has been studied in a sample of 1371 Escherichia coli genes. Correlation and regression analyses show that in- creasing expression levels are accompanied by higher frequencies of base G at first, of base A at second and of base C at third codon positions. However, correla- tion between expressivity and base compositional biases at each codon site was only significant and positive at first codon position. The preference for G-starting codons as gene expression level increases is discussed in terms of translational optimization