Thermally-induced strand cleavage of w794 DNA (144 bp, nucleotide no. 5238–138) after DNA–agent incubation with duocarmycin SA and iso-duocarmycin SA (48 h, 23 °C), removal of unbound agent by EtOH precipitation and 30 min thermolysis (100 °C), followed by denaturing 8% PAGE and autoradiography. Lane 1, control DNA; lanes 2–5, Sanger G, C, A, and T sequencing standards; lanes 6 and 7, (+)-duocarmycin SA and ent-(−)-duocarmycin SA (1, 1 × 10−5 M); lanes 8 and 9, (+)-iso-duocarmycin SA and ent-(−)-iso-duocarmycin SA (5, 1 × 10−5 M).