Analysis of the codon bias in E. coli sequences.

Fifty-three gene sequences from E. coli containing 18,288 reading frame triplets have been characterized according to the nature and level of average codon preference. The distribution of average preferences is bimodal, with approximately half the genes using an average of only 36 codons, and the remainder just 42 codons. There is a high correlation between the level of codon bias, the tRNA population and the abundance of protein product, indicating biased patterns are exploited by the cell for the production of widely different levels of gene product. This relationship is especially striking in genes involved in the production of components for transcription and translation. Overall, the genes for these processes generate some five-fold more protein than the average in the genome, and use about five fewer codons. The very high codon bias found in the RNA polymerase gene thus provides a simple, autogenous mechanism for the coordinate synthesis of these components and RNA polymerase. A surprisingly high level of codon probability is also found in triplets of the complement of coding sequences. This is apparently due to the evolutionary dispersion of coding sequences and/or the requirement for increased levels of secondary structure in messenger RNAs.