Circadian histone acetylation profile of the upstream and core phosphoenolpyruvate carboxylase ( Pepc ) promoter. (A) Transcription levels and (B) histone acetylation under constant illumination (free-running conditions). After a normal 16 h light period, illumination was extended for an additional 40 h without any dark period or temperature shift. Dark periods during previous growth are symbolized by the light grey bar under each chart. The amount of Pepc heterogeneous nuclear RNA was standardized for the amount of Actin-1 mRNA (A). The amount of promoter chromatin precipitated with the antibody indicated in the figure was standardized for the amount of Actin-1 promoter chromatin precipitated with the same antibody. For a better orientation, the 1.0 level is emphasized by a black line. Data for an upstream (-1300 bp) and a core promoter (-200 bp) position are shown. Data points are based on four independent experiments. Vertical lines indicate standard errors.