Journal Article

A Novel HMG A-Like Protein Binds Differentially to the AT-Rich Regions Located in the Far Distal and Proximal Parts of a Soybean Glutamine Synthetase Gene (<i>GS15</i>) Promoter

Michèle Reisdorf-Cren, Elisa Carrayol, Thérèse Tercé-Laforgue and Bertrand Hirel

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 43, issue 9, pages 1006-1016
Published in print September 2002 | ISSN: 0032-0781
Published online September 2002 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcf123
A Novel HMG A-Like Protein Binds Differentially to the AT-Rich Regions Located in the Far Distal and Proximal Parts of a Soybean Glutamine Synthetase Gene (GS15) Promoter

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In soybean (Glycine max L.) ammonium provided externally or as the result of symbiotic nitrogen fixation stimulates the transcription of GS15, a gene encoding cytosolic glutamine synthetase. Strong constitutive positive expression (SCPE), silencer-like and organ-specific elements, located respectively in the distal, the central and the proximal region of the promoter are required to control the ammonium responsiveness of the gene expression [Tercé-Laforgue et al. (1999) Plant Mol. Biol. 39: 551]. It was hypothesized that the correct spatial conformation of the promoter permitted the cooperative action of these three cis-acting elements. Further investigations were therefore required to ascertain this hypothesis. A nodule nuclear protein, binding to a 66 bp AT-rich DNA fragment containing a 13 bp AT-rich repeated sequence (AT-1) and located just downstream of the SCPE element, was identified using a gel retardation assay. A cDNA clone likely to code for this protein was isolated using the yeast one-hybrid system. It encodes a novel DNA binding protein (AT-1SNBP) similar to HMG A proteins but exhibiting a higher molecular weight. AT-1SNBP appears to be encoded by a single gene that is expressed in roots, root nodules and leaves of soybean. Since two other 13 bp AT-rich repeated sequences (AT-2 and AT-3) were localized in the organ-specific element, we have quantified the binding affinity of AT-1SNBP to these sequences. We demonstrate that AT-1SNBP binds differentially to DNA fragments containing AT-1, AT-2 and AT-3 and that its binding affinity depends on the presence of adjacent sequences. This result suggests that AT-1SNBP may be an architectural protein involved in maintaining the spatial conformation of the GS15 promoter, thus facilitating the interaction between the distal and proximal regulatory elements.

Keywords: Keywords: AT hook — AT-rich tracks — Glutamine synthetase — HMG A like — Soybean.; Abbreviations: CaMV, cauliflower mosaic virus; GUS, β-glucuronidase; HMG, high-mobility group; GS, glutamine synthetase.

Journal Article.  8454 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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