Dynamics of global histone acetylation and deacetylation in vivo: rapid restoration of normal histone acetylation status upon removal of activators and repressors.

DNA-binding activators and repressors recruit histone acetylases and deacetylases to promoters, thereby generating localized domains of modified histones that influence transcriptional activity. At the end of a transcriptional response, alterations in histone acetylation status are reversed, but the dynamics of this process are poorly understood. Here, we recruit histone deacetylases and acetylases to a well-defined yeast promoter in a regulated manner. Following dissociation of the recruiting protein from the promoter, targeted deacetylation and acetylation are reversed with rapid, yet distinct, kinetics. Reversal of targeted deacetylation occurs within 5-8 min, whereas reversal of targeted acetylation is more rapid, taking 1.5 min. These findings imply that untargeted, globally acting enzymes generate a highly dynamic equilibrium of histone acetylation and deacetylation reactions across chromatin. Targeted acetylases and deacetylases can locally perturb this equilibrium, yet once they are removed, the global activities mediate a rapid return to the steady-state level of histone acetylation. Our results also indicate that TBP occupancy depends on the presence of the activator, not histone acetylation status.