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In the absence of copper, DsbS acts as a phosphatase toward DsbR, blocking the transcription of Dsb genes. In the presence of copper, the metal ion directly binds to the sensor domain of DsbS, and the Cys82 residue plays a critical role in this process. The copper-binding behavior appears to inhibit the phosphatase activity of DsbS, leading to the activation of DsbR and thus for copper resistance of Pseudomonas aeruginosa, an important human pathogen. [Display omitted] In nature, bacteria must sense copper and tightly regulate gene expression to evade copper toxicity. Here, we identify a new copper-responsive two-component system named DsbRS in the important human pathogen Pseudomonas aeruginosa ; in this system, DsbS is a sensor histidine kinase, and DsbR, its cognate response regulator, directly induces the transcription of genes involved in protein disulfide bond formation (Dsb) (i.e., the dsbDEG operon and dsbB). In the absence of copper, DsbS acts as a phosphatase toward DsbR, thus blocking the transcription of Dsb genes. In the presence of copper, the metal ion directly binds to the sensor domain of DsbS, and the Cys82 residue plays a critical role in this process. The copper-binding behavior appears to inhibit the phosphatase activity of DsbS, leading to the activation of DsbR. The copper resistance of the dsbRS knock-out mutant is restored by the ectopic expression of the dsbDEG operon, which is a DsbRS major target. Strikingly, cognates of the dsbRS - dsbDEG pair are widely distributed across eubacteria. In addition, a DsbR-binding site, which contains the consensus sequence 5′-TTA-N 8 -TTAA-3′, is detected in the promoter region of dsbDEG homologs in these species. These findings suggest that the regulation of Dsb genes by DsbRS represents a novel mechanism by which bacterial cells cope with copper stress. [ABSTRACT FROM AUTHOR]