Figure 7.

Above: cross-linked oligonucleotide duplexes used for enzymatic digestion and LC-MS/MS analysis and stability studies (duplexes used in mass spectrometric studies did not contain the ³²P label). Location of the dA-Ap cross-links is indicated with the line (\). Below: dissociation of the purified cross-link in duplex A incubated in 50 mM HEPES (pH 7.0) and 100 mM NaCl at 37°C for 0, 0.25, 1, 2, 5, 10, 15 and 21 days (lanes 1–8). Following incubation for the specified time, DNA in the samples was ethanol precipitated, washed and stored at –20°C until analysis by 20% denaturing gel electrophoresis. The amount of remaining cross-link at each time point was quantitatively measured by phosphorimager analysis.