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Journal of Bacteriology, May 2000, p. 2649-2653, Vol. 182, No. 9
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
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
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
-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).
-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
-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.
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