EFFECTS OF HISTONE ACETYLATION ON CHROMATIN STRUCTURE

The effect of histone acetylation was monitored on CHO chromatin struc ture, following the addition of 7 mM Na-butyrate to the cell culture m edium. The properties of both control and hyperacetylated chromatins a nd nuclei were investigated by circular dichroism, ethidium bromide in tercalation, differential scanning calorimetry, and affinity chromatog raphy. Our results are compatible with modest but significant alterati ons in the various levels of chromatin organization, as a result of th e charge neutralization of some lysine residues within the N-terminal region of the histonic octamer. Namely, large statistically significan t differences do exist in the heat capacity thermograms of native nucl ei, where unfolding into single nucleofilament of the highly packed na tive chromatin superfiber appears associated with acetylation; at the same time CD, EE, and affinity chromatography point to modest but cons istent differences in I-he compactness of isolated nucleosomes and pol ynucleosomes. (C) 1997 Wiley-Liss,Inc.