The effects of mRNA structure on the activities of the constructs. The activity of β-galactosidase fused with original sequences E1, E5 and C7 was compared to the activities of variants containing synonymous substitutions (marked with asterisks). The nucleotide sequences of the constructs are shown. The expression of β-galactosidase marker protein was measured 3 h after induction with IPTG in the absence and presence of the corresponding antibiotic. The activity of each construct is shown as a ratio of Miller units measured in the absence and presence of antibiotic.