Amino acid contacts between histones are the same for plants and mammals. Binding-site studies using ultraviolet light and tetranitromethane.

Leek chromatin has been cross-linked by UV light and tetranitromethane. The same major H2A--H2B and H2B--H4 cross-linked dimers are formed as in mammalian chromatin. CNBr peptide mapping shows that the cross-links occur in the same regions of the histone sequence for both plants and mammals. Interspecies complexes formed between leek and calf H2A and H2B can be cross-linked by UV light with the same specificity as intraspecies H2A--H2B complexes. We conclude that certain geometric features of histone-histone binding sites are conserved precisely during evolution despite large changes in the overall histone sequence. Moreover, our data show that identification of cross-linked amino acids using binding-site probes such as UV light and tetranitromethane can yield significant information about thermodynamically important contacts within histone-histone binding sites.