Postsynthetic acetylation of histones during the cell cycle: a general function for the displacement of histones during chromatin rearrangements

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Abstract
Postsynthetic acetylation of core histones exhibits a peak during S-phase of the Physarum cell cycle. The maximum 3H-acetate incorporation precedes the maximum of hi stone synthesis. Acetate is incorporated into all core histones during S-phase, but only into H2A and H2B during G2-per1od. Resolution of acetylated H4-subspecies reveals acetate incorporation into preexisting H4, but not into newly synthesized molecules during mitosis and early S-phase. In a prota-m1ne competition assay histones from S-phase chromatin are released at lower protamine concentrations as compared to the lower acetylated G2-chromation. We demonstrate a preferential release of highly acetylated H4-subspecies at low protamine concentrations. Our results fit into a general model of the relationship between histone acetylation and chromatin assembly. According to this model acetylation of core histones would serve as a signal for displacement of histones from nucleosomes by modulating hi stone-protein or h1stone-DNA Interactions. We propose that this mechanism operates during DNA-replication and transcription, as well as during other chromatin rearrangements.