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J. Biol. Chem., Vol. 279, Issue 10, 9037-9042, March 5, 2004

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The Escherichia coli Transcriptional Regulator MarA Directly Represses Transcription of purA and hdeA^*

Thamarai Schneiders, Teresa M. Barbosa, Laura M. McMurry, and Stuart B. Levy¶||

From the Center for Adaptation Genetics and Drug Resistance and the Departments of Molecular Biology and Microbiology and of ^¶Medicine, Tufts University School of Medicine, Boston, Massachusetts 02111

The Escherichia coli MarA protein mediates a response to multiple environmental stresses through the activation or repression in vivo of a large number of chromosomal genes. Transcriptional activation for a number of these genes has been shown to occur via direct interaction of MarA with a 20-bp degenerate asymmetric "marbox" sequence. It was not known whether repression by MarA was also direct. We found that purified MarA was sufficient in vitro to repress transcription of both purA and hdeA. Transcription and electrophoretic mobility shift experiments in vitro using mutant promoters suggested that the marbox involved in the repression overlapped the -35 promoter motif and was in the "backward" orientation. This organization contrasts with that of the class II promoters activated by MarA, in which the marbox also overlaps the -35 motif but is in the "forward" orientation. We conclude that MarA, a member of the AraC/XylS family, can act directly as a repressor or an activator, depending on the position and orientation of the marbox within a promoter.

Received for publication, December 11, 2003 , and in revised form, December 22, 2003.

^* This work was supported principally by National Institutes of Health Grants GM51661/AI56021. 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.

Supported in part by Subprograma Ciência e Tecnologia do 2° Quadro Comunitário de Apoio-PRAXIS XXI/BPD/22065/99, Portugal. Present address, Instituto de Tecnologia Química e Biológica, Avenida da República, Apartado 127, 2781-901 Oeiras Codex, Portugal.

^|| To whom correspondence should be addressed: Center for Adaptation Genetics and Drug Resistance, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111. Tel.: 617-636-6764; Fax: 617-636-0458; E-mail: stuart.levy{at}tufts.edu.

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