Chromatin subunits contain normal levels of major acetylated histone species.

Chromatin subunits or nucleosomes prepared by micrococcal nuclease digestion of nuclei from trout testis have been examined for the presence of in vivo modified histone species. Both monomers and multimers are labeled when testis cells are incubated in the presence of [14C]acetate, but the level of radioactivity in the monomer fraction is 10 to 20% higher than in the multimer fraction. This difference is attributed to the trimming of nucleotides from the monomer DNA, associated with the loss of H1. The specific activities of the [14C]acetate label in histones H2A, H2B, H3, and H4 in monomer particles are similar to their respective values in whole chromatin. Starch gel electrophoresis of histone fractions derived from monomeric nucleosomes revealed the presence of monoacetylated and phosphorylated species of H2A, monoacetylated species of H2B and H3, and mono-, di-, tri-, and tetraacetylated species of H4. No differences in the content of these species between monomeric nucleosomes and whole chromatin could be discerned.