Intracellular binding of ethidium studied by photoaffinity labeling in vivo.

The azide analog of 14C-labeled ethidium bromide was mixed with yeast cells and when photolyzed by visible light, formed covalent complexes with all yeast cell organelles. The 14C counts were found in DNA, RNA and protein of yeast subcellular fractions, illustrating the complexity of binding of a drug which appears highly specific in its actions.