Abstract
Osmoregulated transcription from the proU promoter of Escherichia coli has been successfully reconstituted from purified components in a simple in vitro system consisting of plasmid DNA template, RNA polymerase, and nucleotides in the absence of any other protein factor. proU transcription is stimulated by addition of high concentrations of potassium glutamate, the ionic compound accumulated in vivo during hyperosmotic stress. Transcription from the nonosmoregulated promoters beta la, lac, and pepN is inhibited under the same conditions, demonstrating the specificity of potassium glutamate as an inducer of proU transcription. proU transcription requires a circular DNA template, but stable alterations in the degree of supercoiling are unnecessary for this potassium glutamate-dependent signaling. These results agree well with previous data obtained in an S-30 coupled transcription/translation system and suggest that physiological changes in the ionic composition of the intracellular millieu can regulate gene expression.
Highlights
Osmotic Control of proU Transcription Is Mediated through Direct Action of Potassium Glutamate on the Transcription Complex*
Osmoregulated transcription from the proU promoter of Escherichia coli has been successfully reconstituted from purified components in a simple in vitro system consisting of plasmid DNA template, RNA polymerase, and nucleotides in the absence of any other protein factor. proU transcription is stimulated by addition of high concentrations of potassium glutamate, the ionic compound accumulated in vivo during hyperosmotic stress
The bacterium Escherichia coli can survive in a wide variety of environments due to its ability to rapidly adapt to changing conditions via a repertoire of stress responses
Summary
Osmotic Control of proU Transcription Is Mediated through Direct Action of Potassium Glutamate on the Transcription Complex*. ProU transcription requires a circular DNA template, but stable alterations in the degree of supercoiling are unnecessary for this potassium glutamate-dependent signaling. These results agree well with previous data obtained in an S-30 coupled transcription/translation system and suggest that physiological changes in the ionic composition of the intracellular millieu can regulate gene expression. A subsequent response to hyperosmotic conditions is the replacement of K’ with particular organic osmolytes known as osmoprotectants These compounds, principally glycine betaine [7] and trehalose [8], are less injurious to the cell than are equivalent concentrations of K’ [9, 10].
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