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Journal of Bacteriology, February 2004, p. 631-637, Vol. 186, No. 3
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.3.631-637.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Reversible Acyl-Homoserine Lactone Binding to Purified Vibrio fischeri LuxR Protein

M. L. Urbanowski,1 C. P. Lostroh,2 and E. P. Greenberg1*

Department of Microbiology and W. M. Keck Microbial Communities and Cell Signaling Program, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242,1 Department of Biology, The Colorado College, Colorado Springs, Colorado 809032

Received 9 September 2003/ Accepted 27 October 2003

The Vibrio fischeri LuxR protein is the founding member of a family of acyl-homoserine lactone-responsive quorum-sensing transcription factors. Previous genetic evidence indicates that in the presence of its quorum-sensing signal, N-(3-oxohexanoyl) homoserine lactone (3OC6-HSL), LuxR binds to lux box DNA within the promoter region of the luxI gene and activates transcription of the luxICDABEG luminescence operon. We have purified LuxR from recombinant Escherichia coli. Purified LuxR binds specifically and with high affinity to DNA containing a lux box. This binding requires addition of 3OC6-HSL to the assay reactions, presumably forming a LuxR-3OC6-HSL complex. When bound to the lux box at the luxI promoter in vitro, LuxR-3OC6-HSL enables E. coli RNA polymerase to initiate transcription from the luxI promoter. Unlike the well-characterized LuxR homolog TraR in complex with its signal (3-oxo-octanoyl-HSL), the LuxR-30C6-HSL complex can be reversibly inactivated by dilution, suggesting that 3OC6-HSL in the complex is not tightly bound and is in equilibrium with the bulk solvent. Thus, although LuxR and TraR both bind 3-oxoacyl-HSLs, the binding is qualitatively different. The differences have implications for the ways in which these proteins respond to decreases in signal concentrations or rapid drops in population density.

* Corresponding author. Mailing address: Department of Microbiology, EMRB, University of Iowa, Iowa City, IA 52242. Phone: (319) 335-7775. Fax: (319) 335-7949. E-mail: everett-greenberg{at}uiowa.edu.

Journal of Bacteriology, February 2004, p. 631-637, Vol. 186, No. 3
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.3.631-637.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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