The determinant of plasmid pRJ1004 encodes inducible resistance to the trace element copper. The identification of two copper-dependent transcriptional initiation regions within that each contain a similar upstream hyphenated dyad motif is described. Deletion constructs showed that this “copper box” motif was essential for copper-inducible activity at both pco promoters, P and P The placement of the motif differs in the two promoters, and P contains an extended -10 nonamer typical of promoters for which RNA polymerase does not bind specifically to -35 sequences. P does not contain this motif and is the more strongly expressed promoter. The transcript from P contains the genes, while expresses only The induction profiles for and P fusions were flattened sigmoidal curves with a gradual response to increasing copper concentration. On high-copy-number plasmids, zinc was found also to induce transcription from both promoters Both promoters showed inducible activity in the absence of the plasmid-borne two-component regulatory system, indicating that a second trans-acting regulatory system is present on the chromosome. The product showed repressor action in the absence of while still allowing induction, suggesting the chromosome encoded a similar two-component system to Tn insertion mutagenesis identified chromosomal genes which affected promoter expression, including (sugar phosphotransferase system) and cya (adenylate cyclase). The results support that idea that -encoded copper resistance is an auxiliary mechanism for handling copper, the regulation of which is integrated with the chromosomal regulation of cellular copper metabolism.


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