Binding of Ethidium Bromide Causes Dissociation of the Nucleosome Core Particle

The binding of ethidium bromide to chicken erythrocyte core particles results in a step-wise dissociation of the structure that involves the initial release of one copy each of histones H2A and H2B. Quantitation of the dissociated DNA reveals that a critical amount of drug is required for the dissociation. Above the critical value, the dissociation is time dependent, reversible, and independent of DNA concentration.