Uranyl Photofootprinting

The uranyl-(VI) cation (UO₂ ²⁺ ) forms strong complexes with accessible phosphates of nucleic acid (DNA and RNA) backbones. Upon excitation with long wavelength ultraviolet light (λ = 300–420 nm), uranyl ions bound to backbone phosphates oxidize proximal sugars and induce nucleic acid backbone cleavage. Thus the uranyl(VI) ion functions as a very specific and efficient photochemical probe for identifying ligand(protein)-phosphate contacts in nucleic acid complexes as well as potential (high affinity) cation (e.g., Mg²⁺ )-binding sites in folded nucleic acids. Finally, the cleavage modulation of duplex DNA reflects helix conformation in terms of minor groove width, due to preferential affinity/oxidation efficiency for such regions of the DNA helix.