Chromatin core particle obtained by selective cleavage of histones H3 and H4 by clostripain.

A new chromatin core particle characterized by a half-proteolyzed octamer is obtained by controlled digestion of the native core particle by clostripain. The proteolyzed histones correspond to four polypeptide fragments which are tentatively assigned to H2A[4-129], H2B[1-125], H3[27-135] and H4[18-102] on the basis of electrophoretic evidence and the known specificity of clostripain for arginyl residues. Despite the loss of the N-terminal regions of histones H3 and H4, the partially proteolyzed core particle retains the structural conformation of the native one as shown by circular dichroism. As expected, this half-proteolyzed core particle presents an intermediate accessibility to polycations, such as spermidine, in comparison with that observed with the native core particle and a fully proteolyzed core particle. The latter includes the polypeptide fragments H2A[12-129], H2B[21-125], H3[27-135] and H4[20-102].