The negative strand DNA was prepared by the same method as the positive one except that phosphorylated forward primer P-pr-1 andnon-phosphorylated reverse primer pr-2 were used.Panel B is an example for generating a single-base mismatched heteroduplex by annealing two purified single stranded DNAsLane 1, double stranded DNA produced by PCR, pcrAAT or pcrACT;Lane 2, the positive (top) strand ssACT(