title: The structural basis for enhancer-dependent assembly and activation of the AAA transcriptional activator NorR.
abstract: σ(54)-dependent transcription controls a wide range of stress-related genes in bacteria and is tightly regulated. In contrast to σ(70), the σ(54)-RNA polymerase holoenzyme forms a stable closed complex at the promoter site that rarely isomerises into transcriptionally competent open complexes. The conversion into open complexes requires the ATPase activity of activator proteins that bind remotely upstream of the transcriptional start site. These activators belong to the large AAA protein family and the majority of them consist of an N-terminal regulatory domain, a central AAA domain and a C-terminal DNA binding domain. Here we use a functional variant of the NorR activator, a dedicated NO sensor, to provide the first structural and functional characterisation of a full length AAA activator in complex with its enhancer DNA. Our data suggest an inter-dependent and synergistic relationship of all three functional domains and provide an explanation for the dependence of NorR on enhancer DNA. Our results show that NorR readily assembles into higher order oligomers upon enhancer binding, independent of activating signals. Upon inducing signals, the N-terminal regulatory domain relocates to the periphery of the AAA ring. Together our data provide an assembly and activation mechanism for NorR.
authors.affiliation: Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Colney, Norwich, NR4 7UH, UK.
authors.forename: Matt
authors.initials: M
authors.lastname: Bush
authors.forename: Tamaswati
authors.initials: T
authors.lastname: Ghosh
authors.forename: Marta
authors.initials: M
authors.lastname: Sawicka
authors.forename: Iain H
authors.initials: IH
authors.lastname: Moal
authors.forename: Paul A
authors.initials: PA
authors.lastname: Bates
authors.forename: Ray
authors.initials: R
authors.lastname: Dixon
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhang
mesh_terms: D001419:Bacteria / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004269:DNA, Bacterial / Q000378:metabolism; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D009569:Nitric Oxide / Q000378:metabolism; D051877:RNA Polymerase Sigma 54 / Q000235:genetics* / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid; D015534:Trans-Activators / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D015534:Trans-Activators; D009569:Nitric Oxide; D051877:RNA Polymerase Sigma 54