Same Genes, Distinct Lifestyles

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Science  10 Dec 2004:
Vol. 306, Issue 5703, pp. 1862
DOI: 10.1126/science.306.5703.1862d

The continuing efforts and accomplishments of genome sequencers have furnished the raw material for mapping networks of molecular interactions and pathway regulation. Winfield and Groisman use both this new kind of systems analysis and some tried-and-true molecular microbiology to show how homologous parts can evolve and be assembled in distinct ways.

In the Salmonella enterica PmrA/PmrB two-component system, PmrB senses high (0.1 mM) Fe and phosphorylates PmrA, which then activates transcription of genes that mediate resistance to the antibiotic polymixin; low (10 μM Mg is sensed by the PhoP/PhoQ system, which generates PmrD, which then stimulates PmrA. In comparison, Escherichia coli carries homologs (amino acid identity 84 to 93%) of four of these proteins and of PmrD (55%) and can detect both low Mg and high Fe, but these pathways do not interact because PmrD does not talk to PmrA. Substituting the S. enterica version of pmrD restores communication and also the feedback inhibition of PmrA on pmrD transcription. Why does this matter? The S. enterica regulatory network involving PmrA supports virulence in mice, survival in soil, and colonization of chicken macrophages, and thus enables this bacterium to occupy a broader range of niches. — GJC

Proc. Natl. Acad. Sci. U.S.A. 101, 17162 (2004).

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