Differential regulation of the Proteus mirabilis urease gene cluster by UreR and H-NS

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Abstract
Proteus mirabilis, a cause of catheter-associated urinary tract infection, relies on several virulence factors to colonize the urinary tract. Among these, urease contributes to the development of urinary stones resulting from the increase in local pH due to urease-mediated hydrolysis of urea to NH3and CO2. UreR, an AraC-like transcriptional activator, activates transcription of the genes encoding the urease subunits and accessory proteins (ureDABCEFG) in the presence of urea. UreR also initiates transcription of its own gene in a urea-inducible manner by binding to the intergenic region betweenureRandureD. The intergenic region contains poly(A) tracts that appear to be the target of H-NS. It has been shown thatEscherichia coliandP. mirabilisH-NS acts to repress transcription ofureRin anE. colimodel system. It was hypothesized that H-NS represses urease gene expression in the absence of UreR and urea by binding to the intergenic region. To demonstrate this theP. mirabilis hnsgene was cloned and the 15·6 kDa H-NS was overexpressed and purified as amyc-His tail fusion. Using a gel shift assay, purified H-NS-myc-His bound preferentially to a 609 bp DNA fragment containing the entireureR-ureDintergenic region. H-NS and UreR were able to displace each other from theureR-ureDintergenic region. Circular permutation analysis revealed that the intergenic region is bent. Moreover, H-NS recognizes this curvature, binds the DNA fragment and induces further bending of the DNA as shown by a circular ligation assay. The effects of H-NS, urea and temperature (25 vs 37 °C) on urease expression were shown inE. colicontaining anhnsknockout andP. mirabiliswhere expression was increased at 37 °C. Increased transcription from pureRwas seen in theE. coli hnsknockout when temperature was increased from 25 to 37 °C. These findings suggest H-NS and UreR differentially regulate urease in a negative and positive manner, respectively.