title: The flagellar-specific transcription factor, sigma28, is the Type III secretion chaperone for the flagellar-specific anti-sigma28 factor FlgM.
abstract: The sigma(28) protein is a member of the bacterial sigma(70)-family of transcription factors that directs RNA polymerase to flagellar late (class 3) promoters. The sigma(28) protein is regulated in response to flagellar assembly by the anti-sigma(28) factor FlgM. FlgM inhibits sigma(28)-dependent transcription of genes whose products are needed late in assembly until the flagellar basal motor structure, the hook-basal body (HBB), is constructed. A second function for the sigma(28) transcription factor has been discovered: sigma(28) facilitates the secretion of FlgM through the HBB, acting as the FlgM Type III secretion chaperone. Transcription-specific mutants in sigma(28) were isolated that remained competent for FlgM-facilitated secretion separating the transcription and secretion-facilitation activities of sigma (28). Conversely, we also describe the isolation of mutants in sigma(28) that are specific for FlgM-facilitated secretion. The data demonstrate that sigma(28) is the Type III secretion chaperone for its own anti-sigma factor FlgM. Thus, a novel role for a sigma(70)-family transcription factor is described.
authors.affiliation: Institute for Cell and Molecular Biosciences, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK. p.d.aldridge@ncl.ac.uk
authors.forename: Phillip D
authors.initials: PD
authors.lastname: Aldridge
authors.forename: Joyce E
authors.initials: JE
authors.lastname: Karlinsey
authors.forename: Christine
authors.initials: C
authors.lastname: Aldridge
authors.forename: Christopher
authors.initials: C
authors.lastname: Birchall
authors.forename: Danielle
authors.initials: D
authors.lastname: Thompson
authors.forename: Jin
authors.initials: J
authors.lastname: Yagasaki
authors.forename: Kelly T
authors.initials: KT
authors.lastname: Hughes
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D005407:Flagella / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D016296:Mutagenesis; D009154:Mutation; D016133:Polymerase Chain Reaction; D012486:Salmonella typhimurium / Q000166:cytology / Q000235:genetics* / Q000378:metabolism*; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C064971:FliA protein, Bacteria; D018832:Molecular Chaperones; D012808:Sigma Factor; C071266:FlgM protein, Bacteria; D012321:DNA-Directed RNA Polymerases; D001616:beta-Galactosidase