Spectroscopic properties of ethidium monoazide: a fluorescent photoaffinity label for nucleic acids.

The non-covalent binding of ethidium monoazide to nucleic acids is entirely analogous to that of ethidium (binding constant approximately 2-3 X 10(5) M). The ethidium monoazide can be photochemically covalently linked to nucleic acids in high yield, up to 75%, by long wavelength light. The fluorescence of ethidium monoazide and ethidium crosslinked to nucleic acids show the same environmental sensitivity as does the fluorescence of ethidium. These properties of ethidium monoazide indicate its use as a fluorescent photoaffinity label for nucleic acids. Ethidium diazide can be photochemically linked to nucleic acids but appears to have properties substantially different from those of ethidium.