DNA-Protein Interactions in Nucleosomes and in Chromatin

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Abstract
Crosslinking induced by UV irradiation at 254 nm was used to investigate the structure of [calf thymus] chromatin and isolated nucleosomes. The 4 core histones and histone H1 apparently have reactive groups within a bond length of the DNA bases. In nucleosomes depleted of H1, all core histones react similarly with the DNA and form crosslinks. In chromatin, the rate of crosslinking of all histones to DNA is essentially similar. Comparison of mononucleosomes, dinucleosomes and whole chromatin shows that the rate of crosslinking increases significantly with increasing number of connected nucleosomes. The differences in the rate of crosslinking are interpreted in terms of interactions between neighboring nucleosomes on the chromatin fiber, which are absent in an isolated mononucleosome.