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J. Biol. Chem., Vol. 281, Issue 41, 30941-30946, October 13, 2006

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Degradation of Escherichia coli RecN Aggregates by ClpXP Protease and Its Implications for DNA Damage Tolerance^*

Kohji Nagashima, Yoshino Kubota, Tatsuya Shibata, Chikako Sakaguchi, Hideo Shinagawa, and Takashi Hishida¹

From the Laboratory of Genome Dynamics, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871 and BioAcademia, Inc., Osaka 565-0085, Japan

Protein degradation in bacteria plays a dynamic and critical role in the cellular response to environmental stimuli such as heat shock and DNA damage and in removing damaged proteins or protein aggregates. Escherichia coli recN is a member of the structural maintenance of chromosomes family and is required for DNA double strand break (DSB) repair. This study shows that RecN protein has a short half-life and its degradation is dependent on the cytoplasmic protease ClpXP and a degradation signal at the C terminus of RecN. In cells with DNA DSBs, green fluorescent protein-RecN localized in discrete foci on nucleoids and formed visible aggregates in the cytoplasm, both of which disappeared rapidly in wild-type cells when DSBs were repaired. In contrast, in clpX cells, RecN aggregates persisted in the cytoplasm after release from DNA damage. Furthermore, analysis of cells experiencing chronic DNA damage revealed that proteolytic removal of RecN aggregates by ClpXP was important for cell viability. These data demonstrate that ClpXP is a critical factor in the cellular clearance of cytoplasmic RecN aggregates from the cell and therefore plays an important role in DNA damage tolerance.

Received for publication, July 11, 2006 , and in revised form, August 16, 2006.

^* This work was supported by the Yamada Science Foundation, by a grant-in-aid from the Ministry of Education, Science, Sport, and Culture, and by Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency. 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 To whom correspondence should be addressed: Laboratory of Genome Dynamics, Research Inst. for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan. Tel.: 81-6-6879-8318; Fax: 81-6-6879-8320; E-mail: hishida{at}biken.osaka-u.ac.jp.

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