Uranyl Photoprobing of DNA Structures and DrugDNA Complexes

The uranyl(IV) ion (UO₂ ²⁺ ) binds strongly to the phosphates of DNA and, upon irradiation with long wavelength ultraviolet light, the proximal deoxyn-boses are oxidized by the photochemically excited state of the uranyl1 ion, a very strong oxidant (1 ). Thus the uranyl ion is an efficient DNA photocleavage reagent (2 ,3 ) that has been used to study the sequence specific interaction with the phosphates of the DNA backbone of the respective DNA recogintion sites of various proteins, such as the λ-repressor/O_R1 complex (3 ), RNA polymerase-deo P1 promoter of Escherzchza coli (4 ), RNA polymerase/cyclic AMP receptor protein (CRP)-deo P2 promoter of E coli (5 ), CRP/CytR repressor-deo P2 promoter of E. colz (5 ), and transcription factor IIIA/Xenopus 5s internal control region (6 ).