volume 3 no.5 May 1976 Nucleic Acids Research Histone dimers: a fundamental unit in histone assembly

Histone interactions which occur, at moderate ionic strengths, when several types of purified, renatured histones are mixed at equimolar ratios have been studied. The four histones H2A.H2B.H3 and H 4 complex and form dimers. Histone H ^ does not interact with the other four histone types and does not form dimers. Mixing of single histone species with preformed his-tone pairs as well as mixing of two different types of histone pairs, leads to exchange of histones among the pairs and formation of dimers. No trimers are formed. The dimers are in equilibrium with high-molecular weight his-tone structures. The results indicate that histone dimers may serve as a stable inter-mediate in histone assembly. Because each histone type (except H^) can interact with itself as well as with each of the other three histone types we suggest that each histone type should be considered as an interchangeable subunit of a multichain protein in which the dimer species is the most stable structure