Diurnal histone acetylation pattern on the upstream and core phosphoenolpyruvate carboxylase ( Pepc ) promoter. (A) Transcription levels, (B) nucleosome density and (C) histone acetylation in leaves 4 h after illumination (dark green columns), 16 h after illumination (light green columns), or re-etiolated leaves (orange columns), respectively. Values are H3K9, H3K14, H3K18, H3K23, H3K27, H4K5 and H4K16 histone acetylation levels on an upstream (-1300 bp) and a core (-200 bp) promoter position of Pepc. Data are standardized for acetylation levels on the Actin-1 promoter. For better orientation, the 1.0 level is emphasized by a black line. H3C = chromatin precipitated with an antibody to an invariant epitope on histone H3 as an indicator for nucleosome density. Zein = Intergenic region within the Zein gene cluster. Data points are based on four independent experiments. Vertical lines indicate standard errors.