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Journal of Bacteriology, May 2000, p. 2649-2653, Vol. 182, No. 9
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

H-NS Is a Repressor of the Proteus mirabilis Urease Transcriptional Activator Gene ureR

Christopher Coker, Olubunmi O. Bakare, and Harry L. T. Mobley*

Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland 21201

Received 20 December 1999/Accepted 15 February 2000

Expression of Proteus mirabilis urease is governed by UreR, an AraC-like positive transcriptional activator. A poly(A) tract nucleotide sequence, consisting of A6TA2CA2TGGTA5GA6TGA5, is located 16 bp upstream of the sigma 70-like ureR promoter P2. Since poly(A) tracts of DNA serve as binding sites for the gene repressor histone-like nucleoid structuring protein (H-NS), we measured beta -galactosidase activity of wild-type Escherichia coli MC4100 (H-NS+) and its isogenic derivative ATM121 (hns::Tn10) (H-NS-) harboring a ureR-lacZ operon fusion plasmid (pLC9801). beta -Galactosidase activity in the H-NS- host strain was constitutive and sevenfold greater (P < 0.0001) than that in the H-NS+ host. A recombinant plasmid containing cloned P. mirabilis hns was able to complement and restore repression of the ureR promoter in the H-NS- host when provided in trans. Deletion of the poly(A) tract nucleotide sequence from pLC9801 resulted in an increase in beta -galactosidase activity in the H-NS+ host to nearly the same levels as that observed for wild-type pLC9801 harbored by the H-NS- host. Urease activity in strains harboring the recombinant plasmid pMID1010 (encoding the entire urease gene cluster of P. mirabilis) was equivalent in both the H-NS- background and the H-NS+ background in the presence of urea but was eightfold greater (P = 0.0001) in the H-NS- background in the absence of urea. We conclude that H-NS represses ureR expression in the absence of urea induction.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, University of Maryland School of Medicine, 655 W. Baltimore St., Baltimore, MD 21201. Phone: (410) 706-0466. Fax: (410) 706-6751. E-mail: hmobley{at}umaryland.edu.

Journal of Bacteriology, May 2000, p. 2649-2653, Vol. 182, No. 9
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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