H-NS Is a Repressor of the Proteus mirabilis Urease Transcriptional Activator Gene ureR
- 1 May 2000
- journal article
- research article
- Published by American Society for Microbiology in Journal of Bacteriology
- Vol. 182 (9) , 2649-2653
- https://doi.org/10.1128/jb.182.9.2649-2653.2000
Abstract
Expression of Proteus mirabilis urease is governed by UreR, an AraC-like positive transcriptional activator. A poly(A) tract nucleotide sequence, consisting of A 6 TA 2 CA 2 TGGTA 5 GA 6 TGA 5 , is located 16 bp upstream of the ς 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 β-galactosidase activity of wild-type Escherichia coli MC4100 (H-NS + ) and its isogenic derivative ATM121 ( hns ::Tn 10 ) (H-NS − ) harboring a ureR-lacZ operon fusion plasmid (pLC9801). β-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 β-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.Keywords
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