title: Constitutive mutations of the Salmonella enterica serovar Typhimurium transcriptional virulence regulator phoP.
abstract: The PhoP-PhoQ two-component system is necessary for the virulence of Salmonella spp. and is responsible for regulating several modifications of the lipopolysaccharide (LPS). Mutagenesis of the transcriptional regulator phoP resulted in the identification of a mutant able to activate transcription of regulated genes approximately 100-fold in the absence of PhoQ. Sequence analysis showed two single-base alterations resulting in amino acid changes at positions 93 (S93N) and 203 (Q203R). These mutations were individually created, and although each resulted in a constitutive phenotype, the double mutant displayed a synergistic effect both in the induction of PhoP-activated gene expression and in resistance to antimicrobial peptides. The constitutive phoP gene was placed under the control of an arabinose-inducible promoter to examine the kinetics of PhoP-activated gene induction and the resultant modifications of LPS. Gene induction and 2-hydroxymyristate modification of the lipid A were shown to occur within minutes of the addition of arabinose and to peak at 4 h. As the first constitutive mutant of phoP identified, this allele will be invaluable to future genetic and biochemical studies of this and likely other regulatory systems.
authors.affiliation: Department of Microbiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900, USA. gunnj@uthscsa.edu
authors.forename: J S
authors.initials: JS
authors.lastname: Gunn
authors.forename: R K
authors.initials: RK
authors.lastname: Ernst
authors.forename: A J
authors.initials: AJ
authors.lastname: McCoy
authors.forename: S I
authors.initials: SI
authors.lastname: Miller
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D004352:Drug Resistance, Microbial; D015964:Gene Expression Regulation, Bacterial; D008050:Lipid A / Q000378:metabolism; D008070:Lipopolysaccharides / Q000096:biosynthesis*; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009227:Myristic Acids / Q000378:metabolism; D010455:Peptides; D010641:Phenotype; D017354:Point Mutation; D012486:Salmonella typhimurium / Q000235:genetics* / Q000472:pathogenicity; D017386:Sequence Homology, Amino Acid; D012703:Serotyping; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics*; D015533:Transcriptional Activation
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D008050:Lipid A; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D009227:Myristic Acids; C079793:PagD protein, Salmonella; D010455:Peptides; D015534:Trans-Activators; D014157:Transcription Factors; C112177:osmolarity response regulator proteins; C061064:PhoP protein, Bacteria; C017418:alpha-hydroxymyristic acid