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Journal of Bacteriology, September 2004, p. 5730-5740, Vol. 186, No. 17
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.17.5730-5740.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Mutations Altering the N-Terminal Receiver Domain of NRI (NtrC) That Prevent Dephosphorylation by the NRII-PII Complex in Escherichia coli

Augen A. Pioszak and Alexander J. Ninfa*

Department of Biological Chemistry, University of Michigan Medical School, University of Michigan, Ann Arbor, Michigan

Received 19 April 2004/ Accepted 27 May 2004

The phosphorylated form of NRI is the transcriptional activator of nitrogen-regulated genes in Escherichia coli. NRI~P displays a slow autophosphatase activity and is rapidly dephosphorylated by the complex of the NRII and PII signal transduction proteins. Here we describe the isolation of two mutations, causing the alterations {Delta}D10 and K104Q in the receiver domain of NRI, that were selected as conferring resistance to dephosphorylation by the NRII-PII complex. The mutations, which alter highly conserved residues near the D54 site of phosphorylation in the NRI receiver domain, resulted in elevated expression of nitrogen-regulated genes under nitrogen-rich conditions. The altered NRI receiver domains were phosphorylated by NRII in vitro but were defective in dephosphorylation. The {Delta}D10 receiver domain retained normal autophosphatase activity but was resistant to dephosphorylation by the NRII-PII complex. The K104Q receiver domain lacked both the autophosphatase activity and the ability to be dephosphorylated by the NRII-PII complex. The properties of these altered proteins are consistent with the hypothesis that the NRII-PII complex is not a true phosphatase but rather collaborates with NRI{approx}P to bring about its dephosphorylation.

* Corresponding author. Mailing address: Department of Biological Chemistry, University of Michigan Medical School, 1301 E. Catherine, Ann Arbor, MI 48109-0606. Phone: (734) 763-8065. Fax: (734) 763-4982. E-mail: aninfa{at}umich.edu.

Journal of Bacteriology, September 2004, p. 5730-5740, Vol. 186, No. 17
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.17.5730-5740.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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