Isolated DNA–peptide crosslinks. DNA– peptide crosslinks were obtained using either γ-HOPdG-adducted 12-mer (A), or γ-HOPdG-adducted 30-mer (B), or γ-HOPdA-adducted 12-mer (C). Following to purification, DNA–peptide crosslinks were tested for purity by PAGE under denaturing conditions (in the presence of 8 M urea). DNAs shown are: (M) oligodeoxynucleotide sizing markers, (1) oligodeoxynucleotides adducted with either γ-HOPdG or γ-HOPdA, and (2) corresponding oligodeoxynucleotides modified with the reduced KWKK crosslink.