A variation of the footprinting technique in which a DNA molecule is cleaved at a site occupied by a binding protein. A metal chelator (e.g. ethylenediaminetetra-acetate (EDTA)) is covalently attached to an amino acid residue of the binding protein; Fe³⁺ is ligated to the modified binding-protein-DNA complex and reduced in situ to generate free radicals that cleave the DNA in the immediate vicinity. A DNA sequencing gel ladder subsequently indicates the site of binding.