title: PhoP-induced genes within Salmonella pathogenicity island 1.
abstract: The invasive pathogen Salmonella enterica has evolved a sophisticated device that allows it to enter nonphagocytic host cells. This process requires the expression of Salmonella pathogenicity island 1 (SPI-1), which encodes a specialized type III protein secretion system (TTSS). This TTSS delivers a set of effectors that produce a marked rearrangement of the host cytoskeleton, generating a profuse membrane ruffling at the site of interaction, driving bacterial entry. It has been shown that the PhoP/PhoQ two-component system represses the expression of the SPI-1 machinery by down-regulating the transcription of its master regulator, HilA. In this work, we reveal the presence of a PhoP-activated operon within SPI-1. This operon is composed of the orgB and orgC genes, which encode a protein that interacts with the InvC ATPase and a putative effector protein of the TTSS, respectively. Under PhoP-inducing conditions, expression of this operon is directly activated by the phosphorylated form of the response regulator, which recognizes a PhoP box located at the -35 region relative to the transcription start site. Additionally, under invasion-inducing conditions, orgBC expression is driven both by the prgH promoter, induced by the SPI-1 master regulator HilA, and by the directly controlled PhoP/PhoQ promoter. Together, these results indicate that in contrast to the rest of the genes encompassed in the SPI-1 locus, orgBC is expressed during and after Salmonella entry into its host cell, and they suggest a role for the products of this operon after host cell internalization.
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR-CONICET), Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas (UNR), Suipacha 531, S2002LRK Rosario, Argentina.
authors.forename: Andrés
authors.initials: A
authors.lastname: Aguirre
authors.forename: María Laura
authors.initials: ML
authors.lastname: Cabeza
authors.forename: Silvana V
authors.initials: SV
authors.lastname: Spinelli
authors.forename: Michael
authors.initials: M
authors.lastname: McClelland
authors.forename: Eleonora
authors.initials: E
authors.lastname: García Véscovi
authors.forename: Fernando C
authors.initials: FC
authors.lastname: Soncini
mesh_terms: D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000502:physiology*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D018983:DNA Footprinting; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D017930:Genes, Reporter; D044404:Genomic Islands / Q000235:genetics*; D008969:Molecular Sequence Data; D009876:Operon / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012486:Salmonella typhimurium / Q000235:genetics*; D024363:Transcription Initiation Site; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; C061064:PhoP protein, Bacteria; D001616:beta-Galactosidase