Structures of DNA-protein cross-links induced by bis-electrophiles: N-[2-(guan-7-yl)ethyl]alkylamine adducts formed by mechlorethamine (A); 4-(guan-7-yl)-2,3-butanediol adducts formed by 1,2,3,4-diepoxybutane (B), and 1,1-cis-diammine-2-(5-amino-5-carboxypentyl)amino-2-(2′-deoxyguanosine-7-yl)-platinum(II) adducts induced by cisplatin (C).