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A second positive regulatory function in the mer (mercury resistance) operon.

P Barrineau, A O Summers

|November 1, 1983

Summary

Researchers discovered a new regulatory function in the mer operon, crucial for mercury resistance (Hg(II) uptake). This function, named merC, is essential for producing mercury resistance proteins and depends on the merR regulator.

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Area of Science:

Microbiology
Molecular Biology
Genetics

Background:

The mer operon controls mercury resistance in bacteria.
A known regulatory protein, MerR, positively controls the mer operon.
The exact mechanisms of mer operon regulation are not fully understood.

Purpose of the Study:

To identify and characterize new regulatory elements within the mer operon of the IncFII plasmid R100.
To investigate the function of a newly identified trans-acting positive regulatory element.

Main Methods:

Transpositional mutagenesis of the mer operon.
Analysis of mutant phenotypes, including Hg(II) uptake activity.
Complementation analysis to determine complementation groups.
Mapping of mutations to specific regions of the Hg(II) reductase gene.
Analysis of polypeptide synthesis in minicells.
Comparison with sequence data from related mer operons (e.g., Tn501).

Main Results:

A second trans-acting positive regulatory function was identified, distinct from MerR.
Mutants lacking this function showed no inducible Hg(II) uptake and failed to synthesize mer operon peptides.
Mutations mapped to the N-terminal region of the Hg(II) reductase.
Two new HgCl2-inducible polypeptides of approximately 20 kDa were observed.
Sequence analysis revealed a potential second reading frame (merC) overlapping the Hg(II) reductase gene.

Conclusions:

The identified regulatory function is likely encoded by a distinct gene, merC, with a reading frame superimposed on the Hg(II) reductase gene.
MerC plays a crucial role in the positive regulation of the mer operon, controlling the synthesis of mercury resistance proteins.
The Hg(II) reductase enzyme itself may also possess regulatory activity, or MerC is a separate regulatory protein.

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