Figure 6

Conserved glutamic acids of the ExxE motif in ColS are necessary for metal-promoted activation of a ColR-regulated promoter. β-galactosidase activities measured in P. putida colS-deficient strain complemented with either the wild-type colS (StacS) or the colS variants carrying single substitutions of H35A, E38Q, D57N, H95A, E96Q, H105A, E126Q, E129Q or the double substitutions of E126Q and E129Q under the control of the inducible P_tac promoter. All strains carry the transcriptional fusion of the PP0903 promoter with lacZ in the plasmid p9TT_BlacZ. Bacteria were grown in LB medium containing 0.1 mM IPTG or 0.15 mM FeSO₄ or 0.1 mM IPTG and 0.15 mM FeSO₄ or 0.1 mM IPTG and 0.6 mM ZnSO₄. Data (means with 95% confidence intervals) of at least six independent experiments are presented. Asterisks indicate a statistically significant difference (p < 0.01, Student’s t-test) between the StacS strain and a strain carrying a mutant ColS in a particular medium.