AAG prevents an ICL from forming between an abasic site and P located on opposing strands of a 35mer DNA duplex. A. A 35mer-35mer ICL builds up over time in reactions that contain 0.25 µM duplex 1/3 treated with UDG, but AAG reduces the overall amount of ICL that accumulates. Reactions were carried out at 37 °C and pH 6.5, and samples were quenched and subjected to mild alkaline hydrolysis prior to separation on a 20% denaturing polyacrylamide gel. The slightly higher levels of 35mer present at the earliest time points in reactions containing UDG reveal that the conversion of intact 1/3 to abasic 2/3 is not quite complete at these times. B. The fraction of ICL at time points in A and duplicate reactions is shown. AAG reduces the amount of ICL that forms, with only trace amounts detected when the AAG concentration exceeds the DNA concentration. Lines are exponential fits to the data and give end points of 5% ICL in the absence of AAG, 2.8% ICL in the presence of 0.125 µM AAG, and 0.4% ICL in the presence of 0.5 µM AAG.