Points of contact between histone H1 and the histone octamer.

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Abstract
The topography of the interaction between histone H1 and the histone octamer was investigated. Bovine thymus nuclei or enzymatically fragmented chromatin were treated with 1-ethyl-3(3-dimethylaminopropyl)carbodiimide, which catalyzes the formation of covalent bonds between residues of proteins in electrostatic contact. Histone H1-core histone dimers were identified and the segments of molecules participating in crosslinking were elucidated. The major histone H1-core histone dimer generated upon carbodiimide crosslinking of intact nuclei, chromatin or mononucleosomes consists of the segment of hsitone H1 containing amino acids 74-106 crosslinked to the segment of histone H2A containing amino acids 58-129. The central globular region of histone H1 intimately contacts the histone octamer. Besides histone H1-H2A dimers, 2 other histone H1-containing crosslinked products were detected. In these instances, the segments of histone H1 molecules containing amino acids 1-72 participated in cross-linking. The histone H1 contact points defined here all occur within mononucleosomes and not between nucleosomes. These results permit the formulation of a testable model for the arrangement of histone H1 along polynucleosome chains.
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