Steady-state levels of histone acetylation in Saccharomyces cerevisiae

The importance of control of the levels of histone acetylation for the cont rol of gene expression in eukaryotic chromatin is being elucidated, and the yeast Saccharomyces cerevisiae has proven to be an important model system. The level of histone acetylation in yeast is the highest known. However, o nly acetylation of H4 has been quantified, and reports reveal loss of acety lation in histone preparations. A chaotropic guanidine-based method for his tone isolation from intact wild-type cells or from a single-step nuclear pr eparation with butyrate preserves acetylation of all core histones. Histone H4 has an average of more than 2 acetylated lysines per molecule, distribu ted over 4 sites. Histones H2A, H3, and H2B have 0.2, similar to 2, and >2 acetylated lysines per molecule, respectively, distributed across 2, 5, and 6 sites. Thus, yeast nucleosomes carry, on average, 13 acetylated lysines per octamer, i.e. just above the threshold of 10-12 deduced for transcripti onally activated chromatin of animals, plants, and algae. Following M-r 100 ,000 ultrafiltration in 2.5% acetic acid, yeast histone H3 was purified to homogeneity by reversed-phase high pressure liquid chromatography. Other co re histones were obtained at 80-95% purity.