Sodium butyrate induced structural changes in HeLa cell chromatin.

Postsynthetic modifications of core histones by treatment of HeLa S3 cells with 5mM sodium butyrate lead to alterations in the structure of high molecular weight chromatin. Whole chromatin from butyrate-treated cells, which results in highly acetylated core histones, has an ellipticity [theta]282.5 of 3700 deg cm2 dmol-1 (0.2 mM EDTA, pH 7.4) that is 1200 deg c m2 dmol-1 less than chromatin from untreated HeLa cells, suggesting a more condensed structure. No difference in the circular dichroism spectra was observed in H1-stripped, high molecular weight chromatin obtained from control and butyrate-treated cells at low (0.2 mM EDTA, pH 7.4) ionic strength. Thermal denaturation profiles of high molecular weight chromatin were resolved into three transitions and exhibited a shifting of hyperchromicity from transition I to transitions III, at a higher Tm, with butyrate treatment of HeLa cells, further indicating a more compact structure. Thermal denaturation profiles of H1-stripped chromatin were not affected by butyrate treatment. Ionic strength studies in the range of 0-5 mM NaH2PO4, 0.2 mM EDTA, pH 7.4, of high molecular weight chromatin exhibited a decrease in [theta]282.5 and a shifting of hyperchromicity from transition I to transition III with increasing ionic strength. Control high molecular weight chromatin was more sensitive to changes in ionic strength than its highly acetylated counterpart. These results suggest that acetylation of histones alone does not result in a change in histone-DNA interactions but other changes associated with butyrate treatment most probably cause a more condensed structure, of the fraction studied herein, which is mediated by H1 or other materials removed during stripping in 0.35 M NaCl.