1887

Abstract

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 and mRNA at physiologically significant protein concentrations. AcnA and AcnB synthesis was enhanced by the apo-aconitases and this enhancement was abolished by 3′UTR deletion from the DNA templates, presumably by loss of mRNA stabilization by bound apo-aconitase. studies showed that although total aconitase activity is lowered during oxidative stress, synthesis of the AcnA and AcnB proteins and the stabilities of and 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.

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1999-11-01
2020-03-30
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