Chromatin structure as probed by nucleases and proteases: evidence for the central role of histones H3 and H4.

We have examined the role by each histone in forming the structure of the nu-body. When DNAase I, DNAase II, trypsin and chymotrypsin attack chromatin, characteristic discrete DNA and protein digest fragments are produced. Using this restriction of accessibility as diagnostic for chromatin structure, we have examined complexes of DNA with virtually all possible combinations of histones. The results strongly support our previous conclusion (Camerini-Otero, Sollner-Webb, and Felsenfeld, 1976) that the arginine-rich histones are unique in their ability to create, with DNA a structure with many features of native chromatin. Acting together, slightly lysine-rich histones then modify this complex into one very similar to native chromatin. An analysis of the rate constants of staphylococcal nuclease digestion also confirms that the complex of H3, H4, and DNA is crucial to the structure of the nu-body.