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Sequences Flanking the Hexameric G-Box Core CACGTG Affect the Specificity of Protein Binding

Mary E. Williams, Randy Foster and Nam-Hai Chua
The Plant Cell
Vol. 4, No. 4 (Apr., 1992), pp. 485-496
DOI: 10.2307/3869449
Stable URL: http://www.jstor.org/stable/3869449
Page Count: 12
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Sequences Flanking the Hexameric G-Box Core CACGTG Affect the Specificity of Protein Binding
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Abstract

The CACGTG G-box motif is a highly conserved DNA sequence that has been identified in the 5′ upstream region of plant genes exhibiting regulation by a variety of environmental signals and physiological cues. Gel mobility shift assays using a panel of G-box oligonucleotides differing in their flanking sequences identified two types of binding activity (A and B) in a cauliflower nuclear extract. Competition gel retardation assays demonstrated that the two types of binding activity were distinct. Type A binding activity interacted with oligonucleotides designated as class I elements, whereas type B binding activity interacted strongly with class II elements and weakly with class I elements. A third class of elements, null elements, did not exhibit any detectable binding under our assay conditions. Gel retardation analysis of nonpalindromic hybrid G-box oligonucleotides indicated that hybrid elements of the same class exhibited binding affinity commensurate with the affinity of the weaker element, hybrid class I/II elements exhibited only type B binding, and hybrid class I/null and class II/null elements did not show any detectable binding activity. These binding activities can be explained by the affinity of bZip G-box binding homo- or heterodimer subunits for G-box half sites. These experiments led to a set of classification rules that can predict the binding activity of all reported plant G-box motifs containing the consensus hexameric core. Tissue- and/or development-specific expression of genes containing G-box motifs may be regulated by the affinity of G-box proteins for the different classes of G-box elements.

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