Abstract
The inducibility by organomercury of the broad-spectrum mer operon on pMRA17 cloned from Pseudomonas K-62 plasmid pMR26 was assessed in the absence of a functional merB gene. The mer polypeptides encoded by the mer genes on pMRA17 were almost identified in maxicell induced not only by Hg2+ but also by C6H5Hg+ or CH3Hg+. Maxicell with pMRD103, a merB-deletion plasmid constructed from pMRA17, also produced the corresponding mer polypeptides when maxicell was induced by Hg2+, whereas no mer polypeptides were detected in the maxicell induced by C6H5Hg+ or CH3Hg+. These results suggest that merB is needed for induction of the pMRA17 mer operon expression by organomercurials. Next, to test the inducibility of pMRA17 mer operon expression from its own promoter, a promoterless lacZ was fused with the mer operon, where merB was deleted in plasmid pB43merlacZ. Only Hg2+, but not C6H5Hg+ or CH3Hg+, can activate β-galactosidase expression in bacteria with pB43merlacZ. These results not only imply that the pMRA17 MerR is a narrow-spectrum regulator that did not recognize organomercury as a direct inducer, but also confirms that merB is required for induction of the pMRA17 mer operon expression by organomercurials.
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