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J. Biol. Chem., Vol. 281, Issue 25, 17114-17123, June 23, 2006
Transcription Regulation of ompF and ompC by a Single Transcription Factor, OmpR*From the Department of Biochemistry, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854 The ompF and ompC genes of Escherichia coli are reciprocally regulated by a single transcription factor, phosphorylated OmpR (OmpR-P), depending upon medium osmolarity. This regulation involves activation of ompF and its repression with concomitant activation of ompC. This occurs through OmpR-P binding to four (F1, F2, F3, and F4) and three (C1, C2, and C3) sites located upstream of the ompF and ompC promoters, respectively, through a novel mechanism. Here we show that there is a distinct OmpR-P binding hierarchy within F1, F2, and F3 sites as well as within C1, C2, and C3 sites. Each of these sites contains two tandem 10-bp OmpR-P-binding subsites, a-site and b-site (from 5' to 3' direction). OmpR-P has higher affinity to the downstream b-site than to the upstream a-site in each case. Six OmpR-P molecules bind to F and C sites two-by-two in a discontinuous "galloping" manner. We propose that this tight hierarchical binding of a transcription factor, OmpR, allows distinct stepwise regulation of ompF and ompC transcription, which minimizes their overlapping expression upon changes in the medium osmolarity to achieve the reciprocal expression of ompF and ompC.
Received for publication, March 6, 2006 , and in revised form, April 14, 2006. * This work was supported by Grant GM076587 from the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 These authors contributed equally to this work. 2 To whom correspondence should be addressed: Dept. of Biochemistry, Robert Wood Johnson Medical School, 675 Hoes Ln., Piscataway, NJ 08854. Tel.: 732-235-4115; Fax: 732-235-4559; E-mail: inouye{at}rwja.umdnj.edu.
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