title: OmpR regulates the two-component system SsrA-ssrB in Salmonella pathogenicity island 2.
abstract: Salmonella pathogenicity island 2 (SPI-2) encodes a putative, two-component regulatory system, SsrA-SsrB, which regulates a type III secretion system needed for replication inside macrophages and systemic infection in mice. The sensor and regulator homologs, ssrAB (spiR), and genes within the secretion system, including the structural gene ssaH, are transcribed after Salmonella enters host cells. We have studied the transcriptional regulation of ssrAB and the secretion system by using gfp fusions to the ssrA and ssaH promoters. We found that early transcription of ssrA, after entry into macrophages, is most efficient in the presence of OmpR. An ompR mutant strain does not exhibit replication within cultured macrophages. Furthermore, footprint analysis shows that purified OmpR protein binds directly to the ssrA promoter region. We also show that minimal medium, pH 4.5, induces SPI-2 gene expression in wild-type but not ompR mutant strains. We conclude that the type III secretion system of SPI-2 is regulated by OmpR, which activates expression of ssrA soon after Salmonella enters the macrophage.
authors.affiliation: Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305, USA. aklee@leland.stanford.edu
authors.forename: A K
authors.initials: AK
authors.lastname: Lee
authors.forename: C S
authors.initials: CS
authors.lastname: Detweiler
authors.forename: S
authors.initials: S
authors.lastname: Falkow
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D018272:Porins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000378:metabolism*; D012475:Salmonella / Q000472:pathogenicity*; D013050:Spectrometry, Fluorescence; D015534:Trans-Activators / Q000502:physiology*; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; C113724:OmpC protein; C109237:OmpF protein; D018272:Porins; D012329:RNA, Bacterial; C119761:SsrB protein, Salmonella typhimurium; D015534:Trans-Activators; D014157:Transcription Factors; C112177:osmolarity response regulator proteins; C096222:tmRNA