[Characteristics of the context shift in the frequency of synonymic codons in Escherichia coli].
We have demonstrated, that coding regions of E. coli DNA exhibit the non-random shifts of codon usage frequency depending both on the type of the 3' nucleotide adjacent to the codon and the degree of gene expression. Analysis of primary data--statistics of tetranucleotide occurrences--was performed by the techniques of contingency tables. The results of the investigation allowed us to suggest that the phenomenon observed is connected with the influence of the 3'-adjacent nucleotide on the level of missens-errors and another types of inaccuracy during translation. The specific advantages of such mutations in the third position of the codon are based on the adaptation of the codon to the 3' context in order to increase the efficiency of translation.