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Molecular Characterization of the Growth Phase-Dependent Expression of the lsrA Gene, Encoding Levansucrase of Rahnella aquatilis

Jeong-Woo Seo,^1, Ki-Hyo Jang,² Soon Ah Kang,² Ki-Bang Song,¹ Eun Kyung Jang,³ Buem-Seek Park,¹ Chul Ho Kim,¹ and Sang-Ki Rhee^1*

Korea Research Institute of Bioscience and Biotechnology,¹ RealBioTech Co. Ltd.,³ Department of Medical Nutrition, Graduate School of East-West Medical Science, Kyung Hee University, Suwon 449-701, Korea²

Received 21 February 2002/ Accepted 24 July 2002

Expression of the lsrA gene from Rahnella aquatilis, encoding levansucrase, is tightly regulated by the growth phase of the host cell; low-level expression was observed in the early phase of cell growth, but expression was significantly stimulated in the late phase. Northern blot analysis revealed that regulation occurred at the level of transcription. The promoter region was identified by primer extension analysis. Two opposite genetic elements that participate in the regulation of lsrA expression were identified upstream of the lsrA gene: the lsrS gene and the lsrR region. The lsrS gene encodes a protein consisting of 70 amino acid residues (M_r, 8,075), which positively activated lsrA expression approximately 20-fold in a growth phase-dependent fashion. The cis-acting lsrR region, which repressed lsrA expression about 10-fold, was further narrowed to two DNA regions by deletion analysis. The concerted action of two opposite regulatory functions resulted in the growth phase-dependent activation of gene expression in Escherichia coli independent of the stationary sigma factor ^S.

Present address: Department of Biotechnology, Graduate School of Agriculture and Life Science, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan.

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