On the Use of a Damage-Specific DNA Binding Protein to Probe Lesions in DNA
I never really intended to study a DNA-binding protein at all. I originally set out to purify a pyrimidine dimer-specific endonuclease from human cells, but when the fractions were all collected what I found myself with was a DNA binding protein which bound UV-irradiated, but not nonirradiated, double-stranded DNA. To my surprise, I found that the protein bound perfectly well to photo-reactivated UV-DNA, which indicated that it was recognizing some lesion other than the pyrimidine dimerl. This conclusion was confirmed by studies on the photochemistry of damage introduction. Irradiation of DNA with 313nm light in the presence of acetophenone, a treatment which should result only in triplet state thymine-derived photoproducts (e.g. thymine dimers), yielded essentially no protein-recognizable damage. However, irradiation of either DNA or poly d(A-T) in the presence of acetone, whose triplet state is sufficiently energetic to give energy transfer to all four bases, did give a substrate for the binding protein2. These data seemed to suggest that the protein was recognizing a triplet state-derived adenine (or purine) photoproduct. Life, alas, is never quite that simple.
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