Comparison of the strains with the promoters P_cat, P_cat -10CATTTA or P_cat -10CAGCCA expressing TetR.

<p>(A) Dose-response curve of the promoter variants (P_tetA<i>gfp+</i> with P_cat/P_cat -10CATTTA/P_cat -10CAGCCA <i>tetR</i>) which were incubated with increasing dox concentrations. The control strains, <i>Salmonella</i> WT and the strain lacking TetR resulting in constitutive GFP expression (P_tetA<i>gfp+</i>), were incubated without inducer or with 400 nM dox for maximum reporter activity. The bars illustrate the fluorescence intensity which was normalized to a 1 ml culture with OD₅₉₅ = 0.5. The data are a representative set from at least three independent measurements and display the mean ± standard deviation. (B) Western blot analysis of the steady-state levels of TetR expressed either by P_cat, P_cat -10CATTTA or P_cat -10CAGCCA, detected with a polyclonal anti-TetR antibody. <i>Salmonella</i> WT and 20 ng of purified TetR served as controls. For each strain, 20 µg crude protein extracts were loaded (left panel). Additionally, 40 µg crude protein extract from the mutants P_cat -10CATTTA and P_cat -10CAGCCA were also analyzed (right panel). DnaK served as loading control in both blots and was detected with a monoclonal anti-DnaK antibody.