title: On the mechanism of nucleosome unfolding.
abstract: We have studied the relative stabilities to urea denaturation of histone-histone binding interactions as they occur both in chromatin and in histone complexes free in solution. We have used the two zero-length contact-site cross-linking agents, tetranitromethane and UV light, to measure the relative degree of H2B-H4 and H2A-H2B association under various conditions. The two interactions were disrupted coordinately when nuclei were treated with increasing concentrations of urea. In contrast, when histone complex in 2 M NaCl were treated with urea, the H2B-H4 interaction was found to be much less stable than the H2A-H2B interaction. We have shown previously that nucleosomes unfold at low ionic strengths such that the H2B-H4 but not the H2A-H2B interaction is broken in the process. We speculate that the preferential rupture of the H2B-H4 contact is of physiological significance.
mesh_terms: D000818:Animals; D002417:Cattle; D002467:Cell Nucleus / Q000648:ultrastructure*; D006657:Histones / Q000528:radiation effects; D046911:Macromolecular Substances; D009994:Osmolar Concentration; D011487:Protein Conformation; D013774:Tetranitromethane; D013950:Thymus Gland / Q000648:ultrastructure; D014466:Ultraviolet Rays; D014508:Urea
chemical_list: D006657:Histones; D046911:Macromolecular Substances; D014508:Urea; D013774:Tetranitromethane