Activation of the leu-500 promoter by a reversed polarity tetA gene. Response to global plasmid supercoiling.

The Journal of Biological Chemistry
D ChenD M Lilley

Abstract

The leu-500 promoter is inactivated by a mutation in the -10 region but can be activated in topA Escherichia coli and Salmonella strains. We have found that the tetA gene plays a vital role in the topA-dependent activation of a plasmid-borne leu-500 promoter. In previous studies, the leu-500 promoter and tetA gene have been arranged divergently. In this study we have reversed the polarity of the tetA gene, thus locating the leu-500 promoter at the 3' end of tetA. Despite being formally located in the downstream region of tetA, the leu-500 promoter is equally well activated in a topA strain in this environment, even though it is 1.6 kilobase pairs away from the promoter of the reversed tetA gene. Activation of the leu-500 promoter depends on transcription and translation of tetA but is largely insensitive to the function of other transcription units on the plasmid. These results require a change in viewpoint of the role of tetA, from local to global supercoiling. We conclude that transcription of the tetA gene is the main generator of transcription-induced supercoiling that activates the leu-500 promoter. Unbalanced relaxation of this supercoiling leads to a net increase in the negative linking difference of the plasmid globally...Continue Reading

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Citations

Jan 21, 2011·BMC Systems Biology·Konstantinos BiliourisYiannis N Kaznessis
Dec 10, 1999·Proceedings of the National Academy of Sciences of the United States of America·P Nelson
Oct 19, 2001·Biophysical Journal·S V KuznetsovA Ansari
Oct 8, 1999·Journal of Molecular Biology·A S KrasilnikovS M Mirkin

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