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J. Biol. Chem., Vol. 279, Issue 33, 34406-34410, August 13, 2004

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Effects of Inorganic Polyphosphate on the Proteolytic and DNA-binding Activities of Lon in Escherichia coli^*

Kazutaka Nomura, Junichi Kato, Noboru Takiguchi, Hisao Ohtake, and Akio Kuroda¶||

From the Department of Molecular Biotechnology, Hiroshima University, Hiroshima 739-8530, Japan, the Department of Biotechnology, Osaka University, Osaka 565-0871, Japan, and ^¶PRESTO, Japan Science and Technology Corporation, Kawaguchi, Saitama 332-0012, Japan

Lon belongs to a unique group of proteases that bind to DNA and is involved in the regulation of several important cellular functions, including adaptation to nutritional downshift. Previously, we revealed that inorganic polyphosphate (polyP) increases in Escherichia coli in response to amino acid starvation and that it stimulates the degradation of free ribosomal proteins by Lon. In this work, we examined the effects of polyP on the proteolytic and DNA-binding activities of Lon. An order-of-addition experiment suggested that polyP first binds to Lon, which stimulates Lon-mediated degradation of ribosomal proteins. A polyP-binding assay using Lon deletion mutants showed that the polyP-binding site of Lon is localized in the ATPase domain. Because the same ATPase domain also contains the DNA-binding site, polyP can compete with DNA for binding to Lon. In fact, an equimolar amount of polyP almost completely inhibited DNA-Lon complex formation, suggesting that Lon binds to polyP with a higher affinity than it binds to DNA. Collectively, our results showed that polyP may control the cellular activity of Lon not only as a protease but also as a DNA-binding protein.

Received for publication, April 28, 2004 , and in revised form, June 1, 2004.

^* 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.

^|| To whom correspondence should be addressed: Dept. of Molecular Biotechnology, Hiroshima University, Hiroshima 739-8530, Japan. Tel.: 81-82-424-7758; Fax: 81-82-424-7047; E-mail: akuroda{at}hiroshima-u.ac.jp.

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