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Genetics and Molecular Biology |
Laboratoire de Microbiologie et Génétique Moléculaire, UMR 5100 CNRS – Université Toulouse III, 118 Route de Narbonne, F-31062, Toulouse Cedex, France1
Author for correspondence: Annie Conter. Tel: +33 561 33 58 95. Fax: +33 561 33 58 86. e-mail: aconter{at}ibcg.biotoul.fr
Two overlapping promoters, osmCp1 and osmCp2, direct the transcription of the osmC gene of Escherichia coli. The proximal promoter, osmCp2, is induced upon entry into stationary phase under the control of E
s, the RNA polymerase that uses the s (RpoS) sigma factor. Transcription from the distal promoter, osmCp1, is independent of s. Previous analysis demonstrated that the osmolarity of the growth medium modulates expression of both promoters. The use of an E. coli genomic library showed that the cloned nhaR gene was able to stimulate transcription of an osmC–lac reporter fusion. NhaR is a positive regulator of the LysR family, previously identified as an activator of nhaA, a gene encoding a Na+/H+ antiporter involved in adaptation to Na+ and alkaline pH in E. coli and other enteric bacteria. NhaR was shown to activate only the expression of osmCp1 and to be necessary for the induction of this promoter by LiCl, NaCl and sucrose. Therefore, activation by NhaR is responsible for the osmotic induction of osmCp1. In contrast to its action on nhaA, NhaR activation of osmCp1 is independent of H-NS. Activation of osmCp1 by NhaR requires a site located just upstream of the atypical -35 region of the promoter.
Keywords: transcriptional regulation, osmoregulation, bacterial promoters, NhaR
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