POSTERS - BLAST X - University of Utah

BLAST X Poster #10
EnvZ-OmpR AND CpxA-CpxR REGULATE ompS1 BY DIFFERENTIAL PROMOTER
EXPRESSION
De la Cruz, M.A, Flores-Valdez, M.A., and Calva, E.
Departamento de Microbiología Molecular, Instituto de Biotecnología UNAM Av. Universidad
2001 Col. Chamilpa C.P. 62210 Cuernavaca, Morelos México
The Salmonella enterica ompS1 gene encodes a quiescent porin that belongs to the
OmpC/OmpF family. We recently reported that LeuO, OmpR, H-NS and StpA are regulators of
ompS1 expression. We have now detailed the mechanism of OmpR regulation. In vivo,
phosphorylated OmpR (OmpR-P) showed to be determinant for the regulation of both ompS1
promoters: OmpR-P activated the P1 promoter and repressed the P2 promoter, in an EnvZdependent
manner. In vitro, OmpR-P had a seventy two-fold higher binding-affinity to the
ompS1 promoter region than OmpR, being 2 to 20-fold higher than to the major porin-encoding
ompC and ompF genes, respectively. In addition to EnvZ-OmpR, we found that CpxA-CpxR
positively regulated ompS1 expression. CpxR, together OmpR, was necessary for the activation
of the P1 promoter. CpxR also activated the P2 promoter, but only in the absence of OmpR. Our
model involves LeuO as an antagonist that relieves H-NS and StpA-mediated silencing, allowing
the binding of OmpR and CpxR. High osmolarity and acid pH, or both, stimulated ompS1
expression in an OmpR and CpxR-independent manner, yet dependent on DNA supercoiling.
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