The reactivity of the 2-deoxyribonolactone lesion in single-stranded DNA and its implication in reaction mechanisms of DNA damage and repair

The formal C1'-oxidation product, 2-deoxyribonolactone, is formed as a result of DNA damage induced via a variety of agents, including gamma-radiolysis and the enediyne antitumor antibiotics, This alkaline labile lesion may also be an intermediate during DNA damage induced by copper-phenanthroline. Oligonucleotides containing this lesion at a defined site were formed via aerobic photolysis of oligonucleotides containing a photolabile ketone, and were characterized by gel electrophoresis and electrospray mass spectrometry (ESI-MS), Treatment of oligonucleotides containing the lesion with secondary amines produces strand breaks consisting of 3'-phosphate termini, and products which migrate more slowly in polyacrylamide gels, MALDI-TOF mass spectrometry analysis indicates that the slower moving products are formal adducts of the beta-elimination product resulting from 2-deoxyribonolactone and one molecule of amine, The addition of beta-mercaptoethanol to the reaction mixture produces thiol adducts as well, The stability of these adducts suggests that they cannot be the labile species characterized by gel electrophoresis in copper-phenanthroline-mediated strand scission. The characterization of these adducts by mass spectrometry also provides, by analogy, affirmation of proposals regarding the readivity of nucleophiles with the p-elimination product of abasic sites, Finally, the effects of this lesion and the various adducts on DNA repair enzymes are unknown, but their facile generation from oligonucleotides containing a photolabile ketone suggests that such issues could be addressed.