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 resu lt of DNA damage induced via a variety of agents, including gamma-radiolysi s and the enediyne antitumor antibiotics, This alkaline labile lesion may a lso be an intermediate during DNA damage induced by copper-phenanthroline. Oligonucleotides containing this lesion at a defined site were formed via a erobic photolysis of oligonucleotides containing a photolabile ketone, and were characterized by gel electrophoresis and electrospray mass spectrometr y (ESI-MS), Treatment of oligonucleotides containing the lesion with second ary amines produces strand breaks consisting of 3'-phosphate termini, and p roducts which migrate more slowly in polyacrylamide gels, MALDI-TOF mass sp ectrometry analysis indicates that the slower moving products are formal ad ducts of the beta-elimination product resulting from 2-deoxyribonolactone a nd one molecule of amine, The addition of beta-mercaptoethanol to the react ion mixture produces thiol adducts as well, The stability of these adducts suggests that they cannot be the labile species characterized by gel electr ophoresis in copper-phenanthroline-mediated strand scission. The characteri zation of these adducts by mass spectrometry also provides, by analogy, aff irmation of proposals regarding the readivity of nucleophiles with the p-el imination product of abasic sites, Finally, the effects of this lesion and the various adducts on DNA repair enzymes are unknown, but their facile gen eration from oligonucleotides containing a photolabile ketone suggests that such issues could be addressed.