[Products of limited proteolysis of chromatin core particles]

Limited proteolysis of chromatin and its derivatives with trypsin results in stable fragments of histones containing up to 75% of the original number of amino acid residues. The protein moiety of trypsin-treated core particles from chicken erythrocyte chromatin was characterized. The amino acid analysis of purified histones fragments H2A, H2B and H4 revealed that they are similar to the corresponding products of proteolysis of erythrocyte chromatin histones, whose primary structure has already been established. The sequences 28--135 and 50--135 of histone H3 were identified within the trypsin-treated cord particles and their primary structure was established by peptide mapping. Data from amino acid analysis of the protein moiety of trypsin-treated core particles suggest that the bulk of the low molecular weight products of proteolysis corresponding to the N-terminal parts of histones is removed under conditions which facilitate the maintenance of nucleosomal structure of DNA in trypsin-digested core particles.