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J. Biol. Chem., Vol. 278, Issue 31, 28501-28507, August 1, 2003

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HU Protein of Escherichia coli Has a Role in the Repair of Closely Opposed Lesions in DNA^*

Mitsumasa Hashimoto , Barry Imhoff, Md Moshi Ali and Yoke W. Kow 

From the Department of Radiation Oncology, Emory University, Atlanta, Georgia 30303

Closely opposed lesions form a unique class of DNA damage that is generated by ionizing radiation. Improper repair of closely opposed lesions could lead to the formation of double strand breaks that can result in increased lethality and mutagenesis. In vitro processing of closely opposed lesions was studied using double-stranded DNA containing a nick in close proximity opposite to a dihydrouracil. In this study we showed that HU protein, an Escherichia coli DNA-binding protein, has a role in the repair of closely opposed lesions. The repair of dihydrouracil is initiated by E. coli endonuclease III and processed via the base excision repair pathway. HU protein was shown to inhibit the rate of removal of dihydrouracil by endonuclease III only when the DNA substrate contained a nick in close proximity opposite to the dihydrouracil. In contrast, HU protein did not inhibit the subsequent steps of the base excision repair pathway, namely the DNA synthesis and ligation reactions catalyzed by E. coli DNA polymerase and E. coli DNA ligase, respectively. The nick-dependent selective inhibition of endonuclease III activity by HU protein suggests that HU could play a role in reducing the formation of double strand breaks in E. coli.

Received for publication, April 15, 2003 , and in revised form, May 12, 2003.

^* This work was supported by National Institutes of Health Grant CA 90860. 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.

Present address: Frontier Collaborative Research Center, Tokyo Institute of Technology, Yokohama 226, 8503, Japan.

To whom correspondence should be addressed: Division of Cancer Biology, Dept. of Radiation Oncology, Emory University School of Medicine, 145 Edgewood Ave., Atlanta, GA 30303. Tel.: 404-616-6951; Fax: 404-616-5689; E-mail: ykow{at}emory.edu.

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