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. 2005 Feb;187(3):1124–1134. doi: 10.1128/JB.187.3.1124-1134.2005

FIG. 3.

FIG. 3.

(A) Model for the activation of the PmrA-PmrB two-component system based on the PhoP-PhoQ two-component system in Salmonella. Transcription of the PmrA-activated genes can be induced either by growth in the presence of low magnesium concentrations via the PhoP-PhoQ two-component system that induces transcription of PmrD to activate PmrA or by growth in the presence of high Fe(II) concentrations (or slight acid conditions) independent of PhoP-PhoQ. (Reprinted from reference 24 with permission of the publisher.) (B) Suggested model for activation of the BasR-BasS two-component system in E. coli by a high concentration of extracellular Zn(II). During growth in the presence of high concentrations of Zn(II), BasS senses the cation and activates BasR to induce transcription of a number of genes, some of which are known to be involved in the modification of lipopolysaccharides and, hence, resistance to polymyxin B.