Influence of histone acetylation on the solubility, HI content and DNase I sensitivity of newly assembled chromatin

a novel intermediate in chromatin assembly was described (detected by labeling new DNA in the presence of the deacetylase inhibitor sodium butyrate), which retained-50 % of the heightened sensitivity of newly replicated chromatin to DNasel. It is now reported that nucleosomes replicated in butyrate are considerably more soluble in the presence of magnesium, relative to chromatin replicated under control conditions, and that this heightened magnesium-solubility is reflected in a concomitant increase in the preferential solubility of nucleosomes containing newly synthesized core histones. This differential solubility was accompanied by a 5- to 6-fold depletion of histone HI, and was completely abolished by the selective removal of HI from isolated nuclei. The removal of HI also markedly reduced the preferential DNasel sensitivity of chromatin replicated in butyrate. Further, when mononucleosomes of control and (acetylated) nascent chromatin were compared, no differences in DNasel sensitivity were detected. These results provide evidence that the interactions between newly assembled nucleosomes and histone HI are altered when histone deacetylation is inhibited during chromatin replication, and suggest a mechanism for the control of HI deposition during nucleosome assembly in vivo