Electron microscopic localization of acridine orange binding to DNA within human leukemic bone marrow cells.

An electron microscopic technique has been developed to visualize the binding sites of acridine orange to DNA within fixed human leukemic bone marrow cells. This electron microscopic technique provides both higher resolution and increased chemical specificity for discriminating the nuclear binding sites of acridine orange than does the previous fluorescent light microscopy. Acridine orange binds to DNA exclusively within the active extended euchromatin portion of the cell nucleus. This locale of binding is predicted by the molecular model of gene derepression within interphase mammalian chromatin and correlates with the effects of this ligand on RNA synthesis and on the conversion of euchromatin to heterochromatin by this and other nuclear ligands.