Cis-diamminedichloroplatinum(II) modified DNA stimulates far greater levels of S1 nuclease sensitive regions than does the modification produced by the trans- isomer

S1 endonuclease recognizes distortions in DNA structure produced by both cis- and trans-diamminedichloroplatinum(II) binding. However, cis-(NH₃)₂PtCl₂ binding stimulates far greater levels of S1 digestion than does the trans-isomer. This supports the view that the modes of binding for the two isomers differ and shows that cis-(NH₃)₂PtCl₂ causes a greater disruption of the secondary structure. The S1 digestion products include acid soluble DNA fragments with bound platinum, with the latter providing evidence that (NH₃)₂PtCl₂ is directly responsible for the structural alteration. These findings also reveal that at low levels of binding, the average number of nucleotides excised for each platinum excised in cis-(NH₃)₂PtCl₂ modified DNA is twice as large as for the trans-isomer.