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Gene Review

merR  -  putative transcriptional regulator MerR

Escherichia coli

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Disease relevance of merR

  • Two distinct merR genes, which regulate expression of the mercuric ion resistance gene (mer), of Thiobacillus ferrooxidans strain E-15 have been cloned, sequenced and termed merR1 and merR2 [1].
  • Regulation of transcription in Escherichia coli from the mer and merR promoters in the transposon Tn501 [2].
  • In gram-negative bacteria, two regulatory genes (merR and merD) were identified [3].
  • Here, we report the purification of a Streptomyces lividans thiostrepton-induced transcriptional activator protein, TipAL, whose N-terminus is similar to a family of eubacterial regulatory proteins represented by MerR [4].
  • ZccR--a MerR-like regulator from Bordetella pertussis which responds to zinc, cadmium, and cobalt [5].

High impact information on merR

  • We demonstrate here one such mechanism that employs a single heavy metal receptor protein, MerR, to directly activate transcription of the bacterial mercuric ion resistance operon [6].
  • These differences include the presence of a defense system against superoxide based on manganese ions and a glutathione-dependent system for defense against nitric oxide which is under the control of a novel MerR-like transcriptional regulator [7].
  • Cd(II), Zn(II), Ag(I), Au(I), and Au(III) have been found to partially stimulate transcription in the presence of MerR, but concentrations at least two to three orders of magnitude greater than for Hg(II) are required [8].
  • Transcription mediated by MerR increases from 10% to 90% of maximum in response to a 7-fold change in concentration of HgCl2, consistent with a threshold phenomenon known as ultrasensitivity [8].
  • The trans-acting regulatory gene merR consists of 180 base pairs in both cases and codes for a highly basic polypeptide of 60 amino acids, which is also rich in serine [9].

Chemical compound and disease context of merR


Biological context of merR


Associations of merR with chemical compounds

  • A small region of merR corresponding to residues 81-92 also was mutagenized in a search for other RD mutants and for mutants displaying sufficient transcriptional activation in the absence of mercuric ion to be classified as constitutive activation (CA) mutants [13].
  • Mutations in three of the four cysteine residues of merR resulted in complete loss of Hg(II)-inducible activation but retention of the repressor function, suggesting that these residues serve as ligands for Hg(II) in the activation process [14].
  • The mercury resistance (mer) operon is transcribed from overlapping, divergent promoters: PR for the regulatory gene merR and P(TPCAD) for the structural genes merTPCAD [15].
  • Site-specific insertion and deletion mutants in the mer promoter-operator region of Tn501; the nineteen base-pair spacer is essential for normal induction of the promoter by MerR [16].
  • In vivo DNA methylation of the mer regulatory region (merOP) shows that, with or without the inducer Hg(II), MerR strongly protects four guanine residues in a dyadic region located between the -10 and -35 hexamers of the structural gene promoter (PTPCAD) [17].

Other interactions of merR

  • Expression of the genes was negatively regulated by the product of orf1, now called merR [18].

Analytical, diagnostic and therapeutic context of merR

  • Three different whole cell biosensor constructs were made by fusing the mercury inducible promoter, P(mer), and its regulatory gene, merR, from transposon Tn21 with reporter genes luxCDABE, lacZYA, or gfp [19].
  • Site-directed mutagenesis of clustered acidic residues within the central region of the MerR protein indicated that these residues are important to the protein's ability to repress transcription [13].
  • The K(D) value for binding of mercury(II)chloride to MerR, again determined by mobility shift assay, was 1.1 x 10(-7) M [10].
  • Gel filtration showed that the native MerR is a dimer with a molecular mass of 31 kDa [10].


  1. The merR regulatory gene in Thiobacillus ferrooxidans is spaced apart from the mer structural genes. Inoue, C., Sugawara, K., Kusano, T. Mol. Microbiol. (1991) [Pubmed]
  2. Regulation of transcription in Escherichia coli from the mer and merR promoters in the transposon Tn501. Lund, P.A., Brown, N.L. J. Mol. Biol. (1989) [Pubmed]
  3. Bacterial resistances to inorganic mercury salts and organomercurials. Misra, T.K. Plasmid (1992) [Pubmed]
  4. Autogenous transcriptional activation of a thiostrepton-induced gene in Streptomyces lividans. Holmes, D.J., Caso, J.L., Thompson, C.J. EMBO J. (1993) [Pubmed]
  5. ZccR--a MerR-like regulator from Bordetella pertussis which responds to zinc, cadmium, and cobalt. Kidd, S.P., Brown, N.L. Biochem. Biophys. Res. Commun. (2003) [Pubmed]
  6. The MerR heavy metal receptor mediates positive activation in a topologically novel transcription complex. O'Halloran, T.V., Frantz, B., Shin, M.K., Ralston, D.M., Wright, J.G. Cell (1989) [Pubmed]
  7. Defenses against oxidative stress in Neisseria gonorrhoeae: a system tailored for a challenging environment. Seib, K.L., Wu, H.J., Kidd, S.P., Apicella, M.A., Jennings, M.P., McEwan, A.G. Microbiol. Mol. Biol. Rev. (2006) [Pubmed]
  8. Ultrasensitivity and heavy-metal selectivity of the allosterically modulated MerR transcription complex. Ralston, D.M., O'Halloran, T.V. Proc. Natl. Acad. Sci. U.S.A. (1990) [Pubmed]
  9. Mercuric ion-resistance operons of plasmid R100 and transposon Tn501: the beginning of the operon including the regulatory region and the first two structural genes. Misra, T.K., Brown, N.L., Fritzinger, D.C., Pridmore, R.D., Barnes, W.M., Haberstroh, L., Silver, S. Proc. Natl. Acad. Sci. U.S.A. (1984) [Pubmed]
  10. Purification and characterization of MerR, the regulator of the broad-spectrum mercury resistance genes in Streptomyces lividans 1326. Rother, D., Mattes, R., Altenbuchner, J. Mol. Gen. Genet. (1999) [Pubmed]
  11. DNA distortion mechanism for transcriptional activation by ZntR, a Zn(II)-responsive MerR homologue in Escherichia coli. Outten, C.E., Outten, F.W., O'Halloran, T.V. J. Biol. Chem. (1999) [Pubmed]
  12. The DNA sequence of the mercury resistance operon of the IncFII plasmid NR1. Barrineau, P., Gilbert, P., Jackson, W.J., Jones, C.S., Summers, A.O., Wisdom, S. J. Mol. Appl. Genet. (1984) [Pubmed]
  13. Construction of a synthetic gene for the metalloregulatory protein MerR and analysis of regionally mutated proteins for transcriptional regulation. Comess, K.M., Shewchuk, L.M., Ivanetich, K., Walsh, C.T. Biochemistry (1994) [Pubmed]
  14. Genetic analysis of transcriptional activation and repression in the Tn21 mer operon. Ross, W., Park, S.J., Summers, A.O. J. Bacteriol. (1989) [Pubmed]
  15. Mutations in the alpha and sigma-70 subunits of RNA polymerase affect expression of the mer operon. Caslake, L.F., Ashraf, S.I., Summers, A.O. J. Bacteriol. (1997) [Pubmed]
  16. Site-specific insertion and deletion mutants in the mer promoter-operator region of Tn501; the nineteen base-pair spacer is essential for normal induction of the promoter by MerR. Parkhill, J., Brown, N.L. Nucleic Acids Res. (1990) [Pubmed]
  17. Activator-dependent preinduction binding of sigma-70 RNA polymerase at the metal-regulated mer promoter. Heltzel, A., Lee, I.W., Totis, P.A., Summers, A.O. Biochemistry (1990) [Pubmed]
  18. Regulation of the operon responsible for broad-spectrum mercury resistance in Streptomyces lividans 1326. Brünker, P., Rother, D., Sedlmeier, R., Klein, J., Mattes, R., Altenbuchner, J. Mol. Gen. Genet. (1996) [Pubmed]
  19. Versatile biosensor vectors for detection and quantification of mercury. Hansen, L.H., Sørensen, S.J. FEMS Microbiol. Lett. (2000) [Pubmed]
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