title: Direct evidence for mRNA binding and post-transcriptional regulation by Escherichia coli aconitases.
abstract: Escherichia coli contains a stationary-phase aconitase (AcnA) that is induced by iron and oxidative stress, and a major but less stable aconitase (AcnB) synthesized during exponential growth. These enzymes were shown to resemble the bifunctional iron-regulatory proteins (IRP1)/cytoplasmic aconitases of vertebrates in having alternative mRNA-binding and catalytic activities. Affinity chromatography and gel retardation analysis showed that the AcnA and AcnB apo-proteins each interact with the 3' untranslated regions (3'UTRs) of acnA and acnB mRNA at physiologically significant protein concentrations. AcnA and AcnB synthesis was enhanced in vitro by the apoaconitases and this enhancement was abolished by 3'UTR deletion from the DNA templates, presumably by loss of acn-mRNA stabilization by bound apoaconitase. In vivo studies showed that although total aconitase activity is lowered during oxidative stress, synthesis of the AcnA and AcnB proteins and the stabilities of acnA and acnB mRNAs both increase, suggesting that inactive aconitase mediates a post-transcriptional positive autoregulatory switch. Evidence for an iron-sulphur-cluster-dependent switch was inferred from the more than threefold higher mRNA-binding affinities of the apo-aconitases relative to the holo-enzymes. Thus by modulating translation via site-specific interactions between apo-enzyme and relevant transcripts, the aconitases provide a new and rapidly reacting component of the bacterial oxidative stress response.
authors.affiliation: The Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK1.
authors.forename: Yue
authors.initials: Y
authors.lastname: Tang
authors.affiliation: The Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK1.
authors.forename: John R
authors.initials: JR
authors.lastname: Guest
mesh_terms: D020413:3' Untranslated Regions / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000154:Aconitate Hydratase / Q000502:physiology*; D001059:Apoproteins / Q000502:physiology*; D001483:Base Sequence; D004926:Escherichia coli / Q000502:physiology*; D017353:Gene Deletion; D035941:Iron Regulatory Protein 1; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins / Q000502:physiology; D008969:Molecular Sequence Data; D018384:Oxidative Stress / Q000187:drug effects; D016133:Polymerase Chain Reaction; D011499:Protein Processing, Post-Translational; D012329:RNA, Bacterial / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000502:physiology
chemical_list: D020413:3' Untranslated Regions; D001059:Apoproteins; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D000154:Aconitate Hydratase; D035941:Iron Regulatory Protein 1