Chromatin structure of the Arabidopsis thaliana Adh promoter: analysis of nucleosome positioning

The chromatin structure of the promoter and proximal 5' transcribed region of the Arabidopsis thaliana Adh gene has been studied in three experimental models: whole plants under aerobic conditions in which the gene is repressed, whole plants under flooding-induced anaerobiosis, in which the expression of the gene occurs in some plant tissues and yeast cells in which the Arabidopsis Adh DNA had been cloned but is not expressed at all. Experiments of indirect end labelling after DNase I and micrococcal nuclease digestion of nuclei allowed us to conclude that no positioned nucleosomes exist in plant nuclei on the proximal region of the promoter (up to -350), probably due to the presence of trans acting factors bound to promoter sequences. In the distal regions of the promoter a nucleosome is positioned covering a putative enhancer described by Dolferus et al. (Plant Physiol., 105 (1994) 1075-1087) in the repressed gene, but it is absent from active copies of the gene. Positioning of this nucleosome seems to be directed by sequence, as suggested by the theoretical analysis of the rotational determinants for positioning. Two-dimensional electrophoresis of Arabidopsis DNA indicates that an intrinsic curvature exists roughly between +200 and +350 and this motif directs nucleosome positioning at both sides. (C) 1997 Elsevier Science Ireland Ltd.