Binding of ethidium monoazide to the chromatin in human lymphocytes

The azide analog of 14C]ethidium bromide was mixed with lymphocytes and photolyzed with visible light. The distribution of azide in the chromatin fraction was found to be 55% in DNA, 28% in protein and 16% in RNA. Label in the DNA portion was found to be almost exclusively in the region digestible with micrococcal nuclease. The parent compound, ethidium bromide, competed with azide for binding sites, illustrating that the azide analog mimics the action of ethidium bromide.