Nucleosomes contain DNA binding proteins that resist dissociation by sodium dodecyl sulfate.

A new, rapid, and quantitative method has been developed to show that nucleosomes contain non-histone proteins which are not dissociated by an ionic detergent and are firmly, possibly covalently, bound to DNA. The ability of the method to detect and quantitate the binding of proteins known to form stable (covalent) complexes with DNA has been verified using purified topoisomerase I; in addition, the method will measure DNA/protein adducts formed by ultraviolet light. The distribution of detergent resistant proteins in a population of nucleosomes is non-uniform; the mono- through trimers are depleted of these proteins while higher oligomers are enriched. The data suggest that these proteins are not associated with the nucleosome core but more likely with linker regions between core particles.