DNA distortion mechanism for transcriptional activation by ZntR, a Zn(II)-responsive MerR homologue in Escherichia coli.
MerR-like DNA distortion mechanisms have been proposed for a variety of stress-responsive transcription factors. The Escherichia coli ZntR protein, a homologue of MerR, has recently been shown to mediate Zn(II)-responsive regulation of zntA, a gene involved in Zn(II) detoxification. To determine whether the MerR DNA distortion mechanism is conserved among MerR family members, we have purified ZntR to homogeneity and shown that it is a zinc receptor that is necessary and sufficient to stimulate Zn-responsive transcription at the zntA promoter. Biochemical, DNA footprinting, and in vitro transcription assays indicate that apo-ZntR binds in the atypical 20-base pair spacer region of the promoter and distorts the DNA in a manner that is similar to apo-MerR. The addition of Zn(II) to ZntR converts it to a transcriptional activator protein that introduces changes in the DNA conformation. These changes apparently make the promoter a better substrate for RNA polymerase. We propose that this zinc-sensing homologue of MerR restructures the target promoter in a manner similar to that of other stress-responsive transcription factors. The ZntR metalloregulatory protein is a direct Zn(II) sensor that catalyzes transcriptional activation of a zinc efflux gene, thus preventing intracellular Zn(II) from exceeding an optimal but as yet unknown concentration.
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Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
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O'Halloran
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D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D017931:DNA Primers; D004269:DNA, Bacterial / Q000737:chemistry* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D015533:Transcriptional Activation; D015032:Zinc / Q000378:metabolism*
D001426:Bacterial Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C051124:MerR protein, Bacteria; D011994:Recombinant Proteins; D014157:Transcription Factors; C492246:ZntR protein, E coli; C118628:ZntR protein, bacteria; D015032:Zinc