title: Closing the loop: the PmrA/PmrB two-component system negatively controls expression of its posttranscriptional activator PmrD.
abstract: A fundamental question in biology is how an organism integrates multiple signals to mediate an appropriate cellular response. The PmrAPmrB two-component system of Salmonella enterica can be activated independently by Fe(3+), which is sensed by the PmrB protein, and in low Mg(2+), which is sensed by the PhoQ protein. The low-Mg(2+) activation requires pmrD, a PhoPPhoQ-activated gene that activates the response regulator PmrA at a posttranscriptional level. We now report that pmrD expression is negatively regulated by the PmrAPmrB system. Conditions that activate the PmrA protein independently of pmrD, such as exposure to Fe(3+), resulted in lower levels of pmrD transcription. The PmrA protein footprinted the pmrD promoter upstream of the PhoP-binding site but did not interfere with binding of the PhoP protein. Mutation of the PmrA-binding site in the pmrD promoter abolished PmrA-mediated repression. Negative regulation of the PhoPPhoQ-activated pmrD gene by the PmrAPmrB system closes a regulatory circuit designed to maintain proper cellular levels of activated PmrA protein and constitutes a singular example of a multicomponent feedback loop.
authors.affiliation: Department of Molecular Microbiology, Howard Hughes Medical Institute, Washington University School of Medicine, Campus Box 8230, 660 South Euclid Avenue, St. Louis, MO 63110, USA.
authors.forename: Akinori
authors.initials: A
authors.lastname: Kato
authors.forename: Tammy
authors.initials: T
authors.lastname: Latifi
authors.forename: Eduardo A
authors.initials: EA
authors.lastname: Groisman
mesh_terms: D000595:Amino Acid Sequence; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D005246:Feedback; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000235:genetics; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012486:Salmonella typhimurium / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; C409039:PmrB protein, bacteria; C087732:PmrD protein, Salmonella; D014157:Transcription Factors; C081902:pmrA protein, Bacteria