Localization and in vitro specificity of histone acetylation

Histones of isolated calf thymus chromatin incubated in the presence of [14C]acetyl-CoA are radioactively acetylated, at specific residues. Incubation of calf thymus chromatin with [14C]acetate, however, gives no radioactive acetylation. The distribution of the radioactivity among the histone fractions corresponds well to that observed after incubation of calf thymus nuclei with [14C]acetate. The most striking observation is the complete absence of acetylation of histone F1 in both experiments. The specific activity of histones acetylated in vitro is much greater than that of histones acetylated in calf thymus nuclei, most likely reflecting a smaller degree of dilution of the labelled acetate donor. Investigation of the specificity of acetylation of each histone fraction reveals that for each histone fraction, specific peptides are acetylated in vitro which correspond to the histone peptides acetylated in calf thymus nuclei. Histones F2a1 and F2a2, however, also demonstrate additional minor sites of acetylation in the in vitro studies.