Fig. 3

mRNA and enzyme activity ratio in the integrated strain. a The construct of an artificial operon is illustrated. The order of genes is determined as shown in Fig. 2b. Each gene contains an identical ribosome-binding site, and its expression is regulated by a single temperature-inducible promoter. b mRNA ratio of each gene in the integrated strain is shown. Blue bars indicate the calculated ideal ratio of mRNA for NAD⁺ salvage shown in Fig. 2b (line E), and, red bars indicate the ratio of mRNA measured in the integrated strain. Y axis shows the mRNA ratio in log scale, which is normalized to the expression level of 1st gene encoding NADS. c Enzyme activity in the heat-purified enzyme solution prepared from the integrated strain is shown. Blue bars indicate the optimal enzyme activity ratio for salvage synthesis of NAD⁺ at 60 °C shown in Fig. 2b (line A), and red bars indicate the activity of each enzyme in the integrated strain. Y axis shows enzyme activity in log scale, which is normalized to that of 1st gene encoding NADS. The error bar represents standard error calculated from triplicate measurements