Thermally-induced strand cleavage of w794 DNA following DNA alkylation; DNA–agent incubation at 23 °C for 24 h, removal of unbound agent by EtOH precipitation, and 30 min of thermolysis (100 °C) followed by 8% denaturing PAGE and autoradiography. Lane 1, control DNA; lanes 2–5, Sanger G, C, A, and T sequencing reactions; lanes 6–8, (–)-15 (natural enantiomer at 1 × 10−5, 1 × 10−6, and 1 × 10−7 M−1).