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J. Biol. Chem., Vol. 281, Issue 52, 40208-40215, December 29, 2006

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Specificity of DNA Binding and Dimerization by CspE from Escherichia coli^*

Danielle Johnston, Christine Tavano¹, Sue Wickner, and Nancy Trun²

From the Department of Biological Sciences, Duquesne University, Pittsburgh, Pennsylvania 15282 and the Laboratory of Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20895

The CspE protein from Escherichia coli K12 is a single-stranded nucleic acid-binding protein that plays a role in chromosome condensation in vivo. We report here that CspE binds to single-stranded DNA containing 6 or more contiguous dT residues with high affinity (K_D < 30 nM). The interactions are predominantly through base-specific contacts. When an oligonucleotide contains fewer than 6 contiguous dT residues, the CspE interactions with single-stranded DNA are primarily electrostatic. The minimal length of single-stranded DNA to which CspE binds in a salt-resistant manner is eight nucleotides. We also show that CspE exists as a dimer in solution. We present a possible mechanism to explain the role of CspE in chromosome condensation in vivo by CspE binding to distant DNA regions in the chromosome and dimerizing, thereby condensing the intervening DNA.

Received for publication, July 5, 2006 , and in revised form, October 31, 2006.

^* This work was supported by grants from the National Institutes of Health (Grant GM65121-01), The Winter Foundation, The Hunkele Dreaded Disease Award, and the Intramural Research Program of the NCI, CCR, Center for Cancer Research, 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.

The on-line version of this article (available at http://www.jbc.org) contains a supplemental figure.

¹ Present address: bioMerieux, Duram, NC, 27712.

² To whom correspondence should be addressed: Dept. of Biological Sciences, Duquesne University, 600 Forbes Ave., 256 Mellon Hall, Pittsburgh, PA 15282. Tel.: 412-396-1853; Fax: 412-396-5907; E-mail: trun{at}duq.edu.

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