In a previous study, we have identified four types of 3' terminal codon pairs depending on their frequency of occurrence in the Escherichia coli genome: overrepresented, moderately represented, underrepresented, and missing. In this study, the influence of eight codon pairs belonging to these four groups on the efficiency of chloramphenicol acetyltransferase (cat) gene expression in E. coli is examined. Our results show that the missing codon pairs CCU:UAG (Pro:Stop) and CCC:UAG (Pro: Stop) had decreasing effect, whereas another missing pair CCU:AGG (Pro:Arg) had an opposite effect on the yield of CAT protein in comparison with the wild-type cat gene.