Control of histone acetylation : Cell-cycle dependence of deacetylase activity in Physarum nuclei

Nuclei from naturally synchronous plasmodia of Physarum polycephalum were assayed for histone deacetylase activity. The substrate for the assay was a peptide comprising the amino terminal region (residues 1–23) of calf thymus histone H4. The deacetylase activity per nucleus remained constant during S phase and early G2 phase and then doubled in a linear fashion during mid and late G2 phase reaching its maximum level at metaphase. The data imply that H4 acetylation is linked to prior chromatin structural changes.