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

Abstract

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 Hg2+ functioned as an inducer. In the presence of organomercurial compounds, basal transcription of merB3 was needed to produce inorganic Hg2+ 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 Hg2+ or organomercurials were added. These results show that MerR1 functions as a repressor in the absence of Hg2+ and as an activator in the presence of Hg2+, while MerR2 functions as a repressor. (C) 2002 Elsevier Science B.V. All rights reserved.