Effect of DNase I on histone acetyltransferase and deacetylase enzyme activities in friend cell nuclei: Evidence for a putative inhibitor of the deacetylase enzymes in transcriptionally active chromatin

Abstract

Pancreatic DNase I was used to preferentially destroy the DNA of transcriptionally “active” chromatin in isolated nuclei of normal Friend erythroleukemic mouse cells and in isolated Friend cell nuclei containing high levels of hyperacetylated histones as a result of prior exposure of the cells in culture to sodium butyrate. Histone acetyltransferase and histone deacetylase enzyme assays were performed on these two different populations of treated nuclei and the relative amounts of enzyme activities found were compared with the amounts of similar activities in control cell nuclei not treated with DNase I. The results of such experiments indicate that the relative amount of histone acetyltransferase activity is about the same in all of the tested nuclei regardless of whether they have been exposed to limited digestion with DNase I. On the other hand, the amount of histone deacetylase enzyme activity found in all DNase I-digested nuclei (regardless of their source) is consistently higher (by more than 50%) than the amount of activity found in untreated, control nuclei. These results suggest that limited digestion with the enzyme releases into a soluble supernatant fraction an inhibitor of the histone deacetylase enzymes that is normally present in transcriptionally active chromatin. This conclusion was further reinforced by the results obtained from various supernatant mixing experiments.