Histones H2a, H2b, H3, and H4 form a tetrameric complex in solutions of high salt.

In 2 M NaCl, histones H2b, H2a, H3, and H4 form a heterotypic tetrameric complex made up of one chain of each histone. This complex has been analyzed by hydrodynamic techniques. It is indistinguishable from histones in chromatin by its resistance to trypsin, pattern of reactivity with 125I. and ability to form specific crosslinked products after treatment with formaldehyde. It is proposed that this complex is responsible for protecting the small DNA fragments produced by exhausting nuclease digestion of nuclei and that on the average two of these complexes protect the larger 180-200 base pair unit produced by partial treatment of nuclei with nuclease.