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Gene. 2002 Nov 13;301(1-2):13-20.

Characterization of two regulatory genes of the mercury resistance determinants from TnMERI1 by luciferase-based examination.

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Laboratory of Environmental Biotechnology, Faculty of Engineering, Tohoku Gakuin University, 1-13-1 Chuo, Tagajo-shi, 985-8537, Miyagi, Japan.


The broad-spectrum mercury resistance transposon, TnMERI1, of Bacillus megaterium strain MB1, contains three proposed operator/promoter (O/P) transcriptional start sites and two regulatory genes (merR1 and merR2). A series of luciferase (lux)-based transcriptional fusion plasmids were studied in Escherichia coli to show that both merR1 and merR2 gene products repressed transcription from O/PmerB3, O/PmerR1, and O/PmerR2 under uninduced conditions. Derepression occurred when the merR1 gene was present and Hg(2+) functioned as an inducer. In the presence of organomercurial compounds, basal transcription of merB3 was needed to produce inorganic Hg(2+) as the inducer of expression regulated by MerR1 at O/PmerB3. The presence of merR2 repressed transcription from all three O/Pmer sites under both non-induced conditions and when inorganic Hg(2+) or organomercurials were added. These results show that MerR1 functions as a repressor in the absence of Hg(2+) and as an activator in the presence of Hg(2+), while MerR2 functions as a repressor.

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