ANTHRAQUINONE PHOTONUCLEASES - A SURPRISING ROLE FOR CHLORIDE IN THE SEQUENCE-NEUTRAL CLEAVAGE OF DNA AND THE FOOTPRINTING OF MINOR GROOVE-BOUND LIGANDS

Irradiation of water-soluble anthraquinone (AQ) reagents in the presen ce of chloride ions results in the spontaneous, sequence-neutral cleav age of DNA, Mechanistic studies indicate that cleavage is initiated by chlorine atoms, produced by charge transfer interaction between chlor ide anion and AQ triplet states, High-resolution gel electrophoresis s uggests that cleavage arises from abstraction of a hydrogen atom from C-4' of deoxyribose units. The targeting of this hydrogen, which is lo cated in the minor groove of duplex DNA, can be effectively blocked by netropsin and, to a lesser degree, berenil, leading to photofootprint ing of these minor groove-binding drugs.