(Panel A) Reaction of ECH and Duplex A over time at pH 5.0 (lanes 1-4) and pH 6.0 (lanes 5-8) at 37 °C. Reaction aliquots were taken at time 0 (lanes 1 and 5), 4 h (lanes 2 and 6), 8 h (lanes 3 and 7), and 12 h (lanes 4 and 8). Presumed interstrand cross-links appear as low-mobility bands. (Panel B) Reaction of ECH and Duplex A over time at pH 7.0. Reaction aliquots were taken at time 0 (lane 1), 4 h (lane 2), 8 h (lane 3), and 12 h (lane 4).