Figure 5.

Methylene blue-sensitized photocleavage of PNA(AQ1)/DNA-1X hybrid. Two samples were prepared, each containing 5000 cpm 5′-³²P-end-labeled DNA-1X and 5.0 μM each of unlabeled DNA-1X and PNA in 10 mM sodium phosphate buffer (pH 7.0) with 10 μM methylene blue. The water was evaporated and replaced with D₂O in one case, H₂O in the other. The solvent was evaporated and replaced twice more to minimize the amount of H₂O present in the D₂O sample. Samples were then divided in two; one set of samples was kept in the dark, and the other set was irradiated for 15 min in microcentrifuge tubes with the filtered (λ > 600 nm) output of a 150-W Hg arc lamp. All samples were treated with piperidine after precipitation. Samples for lanes 1 and 3 were kept in the dark, and those for lanes 2 and 4 were irradiated. Control samples lacking methylene blue showed no cleavage of the DNA after irradiation under these conditions (data not shown).