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Journal of Bacteriology, June 2001, p. 3606-3613, Vol. 183, No. 12
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.12.3606-3613.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Maximal Expression of Membrane-Bound Nitrate Reductase in Paracoccus Is Induced by Nitrate via a Third FNR-Like Regulator Named NarR

Nicholas J. Wood,1 Tooba Alizadeh,1 Scott Bennett,1 Joanne Pearce,1 Stuart J. Ferguson,2 David J. Richardson,3 and James W. B. Moir1,*

Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN,1 Department of Biochemistry, University of Oxford, Oxford OX1 3QU,2 and School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ,3 United Kingdom

Received 28 August 2000/Accepted 28 March 2001

Respiratory reduction of nitrate to nitrite is the first key step in the denitrification process that leads to nitrate loss from soils. In Paracoccus pantotrophus, the enzyme system that catalyzes this reaction is encoded by the narKGHJI gene cluster. Expression of this cluster is maximal under anaerobic conditions in the presence of nitrate. Upstream from narK is narR, a gene encoding a member of the FNR family of transcriptional activators. narR is transcribed divergently from the other nar genes. Mutational analysis reveals that NarR is required for maximal expression of the membrane-bound nitrate reductase genes and narK but has no other regulatory function related to denitrification. NarR is shown to require nitrate and/or nitrite is order to activate gene expression. The N-terminal region of the protein lacks the cysteine residues that are required for formation of an oxygen-sensitive iron-sulfur cluster in some other members of the FNR family. Also, NarR lacks a crucial residue involved in interactions of this family of regulators with the sigma 70 subunit of RNA polymerase, indicating that a different mechanism is used to promote transcription. narR is also found in Paracoccus denitrificans, indicating that this species contains at least three FNR homologues.

* Corresponding author. Mailing address: Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom. Phone: 44 (0) 114 2224409. Fax: 44 (0) 114 2728697. E-mail: j.moir{at}sheffield.ac.uk.

Journal of Bacteriology, June 2001, p. 3606-3613, Vol. 183, No. 12
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.12.3606-3613.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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