Role of Zur in the expression of the CC2720-26 operon in response to zinc. (A) Scheme of C. crescentus CC2720-26 locus depicting the putative czrCBA operon organization described in . Gray arrows indicate genes encoding the RND and P-type ATPase transport systems. White arrows indicate hypothetical proteins. (B) β -galactosidase activity assay of CC2720-26 operon in response to zinc availability, in NA1000 (wild type) and MM69 (zur mutant) strains. White bars, M2 medium, light grey bars, M2 containing 500 μM ZnCl2, dark grey bars, M2 containing 500 μM EDTA and black bars, M2 containing both 500 μM ZnCl2 and 500 μM EDTA. Asterisks indicate that the putative Zur binding site into the promoter region of CC2720-26 was mutagenized. The results shown are the average of at least three experiments. Error bars indicate standard deviations. (C) β -galactosidase activity assay of CC2720-26 operon in response to zinc availability in NA1000 and MM69 strains harboring plasmid pUJ142 containing or not the zur gene.