The organization of histones and DNA in chromatin: Evidence for an arginine-rich histone kernel

We have examined the role played by various histones in the organization of the DNA of the nucleosome, using staphylococcal nuclease as a probe of DNA conformation. When this enzyme attacks chromatin, a series of fragments evenly spaced at 10 base pair intervals is generated, reflecting the histone-DNA interactions within the nucleosome structure. To determine what contribution the various histones make to DNA organization, we have studied the staphylococcal nuclease digestion patterns of complexes of DNA with purified histones. Virtually all possible combinations of homogeneous histones were reconstituted onto DNA. Exhaustive digestion of a complex containing the four histones H2A, H2B, H3, and H4 yields a DNA fragment pattern very similar to that of whole chromatin. The only other combinations of histones capable of inducing chromatin-like DNA organization are H2A/H2B/H4 and those mixtures containing both H3 and H4. From an examination of the kinetics of digestion of H3/H4 reconstitutes, we conclude that although the other histones have a role in DNA organization within the nucleosome, the arginine-rich histone pair, H3/H4, can organize DNA segments the length of the nucleosome core in the absence of all other histones.