The OmpR regulons of <i>S.</i> Typhimurium and <i>E. coli</i> in acid pH.

<p>Members of the OmpR regulon in has evolved since the divergence of these closely-related species. OmpR (pairs of circles) binds to a species-specific regulon in <i>Salmonella</i> and <i>E. coli</i>; examples of these targets are shown. In <i>E. coli</i>, OmpR binds to genes involved in acid resistance e.g. <i>cad</i> operon <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1004215#pgen.1004215-Delgado1" target="_blank">[13]</a> and general stress resistance e.g. the <i>uspC </i><a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1004215#pgen.1004215-Alphen1" target="_blank">[14]</a> and <i>emrK </i><a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1004215#pgen.1004215-Sarma1" target="_blank">[15]</a> genes. In <i>S.</i> Typhimurium, OmpR binds to pathogenicity islands SPI-1, -2, and -4, and to genes regulated by PhoP. OmpR positively regulates <i>phoP</i> expression by an unknown mechanism (denoted by the question mark). The genes identified as the core OmpR regulon (conserved targets; bound by OmpR in both species) encode surface-associated organelles and proteins. Modulation of the cell-surface composition may be an important function of the core OmpR regulon in response to acidic stress.