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Gene Review

merA  -  mercuric (ion) reductase

Shigella flexneri 2b

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Disease relevance of merA


High impact information on merA

  • This region included the 3'-terminal part of the merA gene, merD, unidentified reading frame URF1, and a part of URF2 homologous to previously sequenced determinants of plasmid R100 [3].
  • The results indicated that, with increasing gene copy number, there was an approximately 5-fold increase in the merA gene product compared with a 2.5-fold increase in the merT gene product [4].
  • In contrast, the expression level of the mercuric reductase gene underwent higher amplification than that of the transport genes at both the RNA and protein levels as plasmid copy number increased [4].
  • RNA hybridizations indicated that mRNA of the cytoplasmic mercuric reductase (merA gene product) increased 11-fold with the 47-fold gene amplification, while mRNA of the transport protein (merT gene product) increased only 5.4-fold [4].
  • A hybrid mer operon consisting of the merR gene from pDU1358, a hybrid merA gene (determining mercuric reductase enzyme), and lacking the merB gene (determining phenylmercury lyase activity) was inducible by both phenylmercury and inorganic Hg2+ [5].

Biological context of merA

  • Between the merA and merD genes, an open reading frame encoding a 212 amino acid polypeptide was identified as the merB gene that determines the enzyme organomercurial lyase that cleaves the C--Hg bond of phenylmercury [3].

Associations of merA with chemical compounds

  • 5. The T. ferrooxidans mercuric reductase was a soluble enzyme that was dependent upon added NAD(P)H [2].
  • When both fragments were cloned together into a derivative of plasmid ColE1, the hybrid plasmid conferred properties indistinguishable from those of the parental plasmid, NR1: resistance to Hg2+ and to the organomercurials merbromin and fluoresceinmercuric acetate and the inducible synthesis of the enzyme mercuric reductase [6].

Other interactions of merA

  • Mutations affecting the previously described mer genes merR (regulation), merT (transport), and merA (reductase) were characterized [7].
  • The sequences following merC and preceding the next structural gene merA are unrelated between R100 and Tn501 and differ in length, with 72 bp in Tn501 and 509 bp in R100 [8].


  1. Nucleotide sequence of the Thiobacillus ferrooxidans chromosomal gene encoding mercuric reductase. Inoue, C., Sugawara, K., Shiratori, T., Kusano, T., Kitagawa, Y. Gene (1989) [Pubmed]
  2. Mercuric reductase enzyme from a mercury-volatilizing strain of Thiobacillus ferrooxidans. Olson, G.J., Porter, F.D., Rubinstein, J., Silver, S. J. Bacteriol. (1982) [Pubmed]
  3. Cloning and DNA sequence of the mercuric- and organomercurial-resistance determinants of plasmid pDU1358. Griffin, H.G., Foster, T.J., Silver, S., Misra, T.K. Proc. Natl. Acad. Sci. U.S.A. (1987) [Pubmed]
  4. Effect of gene amplification on mercuric ion reduction activity of Escherichia coli. Philippidis, G.P., Malmberg, L.H., Hu, W.S., Schottel, J.L. Appl. Environ. Microbiol. (1991) [Pubmed]
  5. Mercury operon regulation by the merR gene of the organomercurial resistance system of plasmid pDU1358. Nucifora, G., Chu, L., Silver, S., Misra, T.K. J. Bacteriol. (1989) [Pubmed]
  6. Hypersensitivity to Hg2+ and hyperbinding activity associated with cloned fragments of the mercurial resistance operon of plasmid NR1. Nakahara, H., Silver, S., Miki, T., Rownd, R.H. J. Bacteriol. (1979) [Pubmed]
  7. Tn5 insertion mutations in the mercuric ion resistance genes derived from plasmid R100. Ni'Bhriain, N.N., Silver, S., Foster, T.J. J. Bacteriol. (1983) [Pubmed]
  8. Mercuric reductase structural genes from plasmid R100 and transposon Tn501: functional domains of the enzyme. Misra, T.K., Brown, N.L., Haberstroh, L., Schmidt, A., Goddette, D., Silver, S. Gene (1985) [Pubmed]
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