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J. Biol. Chem., Vol. 281, Issue 3, 1345-1351, January 20, 2006

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Inactivation of Homocitrate Synthase Causes Lysine Auxotrophy in Copper/Zinc-containing Superoxide Dismutase-deficient Yeast Schizosaccharomyces pombe^*

From the Laboratory of Molecular Microbiology, School of Biological Sciences, and the Institute of Microbiology, Seoul National University, Seoul 151-742, Korea

The fission yeast Schizosaccharomyces pombe lacking copper/zinc-containing superoxide dismutase (CuZn-SOD) is auxotrophic for lysine and sulfurous amino acids under aerobic growth conditions. A multicopy suppressor gene (phx1⁺) that restored the growth of CuZn-SOD-deficient cells on minimal medium was isolated. It encodes a putative DNA-binding protein with a conserved homeobox domain. Overproduction of Phx1 increased the amount of several proteins, and one of those turned out to be a putative homocitrate synthase (HCS) encoded by the lys4⁺ gene in S. pombe as judged by mass spectrometric analysis. Consistent with this observation, overexpression of the lys4⁺ gene increased HCS enzyme activity and was sufficient to suppress the lysine requirement of the CuZn-SOD-deficient cells. Enzyme activity and Western blot analyses revealed that the activity and protein level of HCS were dramatically reduced upon depletion of CuZn-SOD. Treatment of exponentially growing S. pombe cells with paraquat, a superoxide generator, caused a decrease in the amount of Lys4 protein as expected. These results led us to conclude that HCS, the first enzyme in the -aminoadipate-mediated pathway for lysine synthesis common in fungi and some bacteria, is a labile target of oxidative stress caused by CuZn-SOD depletion and that its synthesis is positively regulated by the putative transcriptional regulator Phx1.

Received for publication, June 17, 2005 , and in revised form, October 5, 2005.

^* This work was supported in part by a grant from the Ministry of Science and Engineering (to J.-H. R.). 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 Supported by Research Fellowship BK21 from the Korean Ministry of Education and Human Resources.

² Present address: Lab. of Biochemical Genetics, NHLBI, NIH, Bethesda, MD 20892.

³ To whom correspondence should be addressed: Lab. of Molecular Microbiology, School of Biological Sciences, Bldg. 18, Rm. 308, Seoul National University, Shillimdong, Kwanak-gu, Seoul 151-742, Korea. Tel.: 82-2-880-6706; Fax: 82-2-888-4911; E-mail: jhroe{at}snu.ac.kr.

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