RADIATION-INDUCED ELECTRON MIGRATION IN NUCLEIC-ACIDS

Radiation-induced electron migration along DNA is a mechanism by which randomly produced stochastic energy deposition events can lead to non -random types of damage along DNA manifested distal to the sites of th e inital energy deposition. Radiation-induced electron migration in nu cleic acids has been examined using oligonucleotides containing 5-brom ouracil (5-BrU). Interaction of 5-BrU with solvated electrons results in release of bromide ions and formation of uracil-5-yl radicals. Moni toring either bromide ion release or uracil formation provides an oppo rtunity to study electron migration processes in model nucleic acid sy stems. Using this approach we have discovered that electron migration along oligonucleotides is significantly influenced by the base sequenc e and strandedness. Migration along 7 base pairs in oligonucleotides c ontaining guanine bases was observed for oligonucleotides irradiated i n solution, which compares with mean migration distances of 6-IObp for Escherichia coli DNA irradiated in solution and 5.5 bp for E. coli DN A irradiated in cells. Evidence also suggests that electron migration can occur prefer entially in the 5' to 3' direction along a double-str anded oligonucleotide containing a region of purine bases adjacent to the 5-BrU moiety. Our continued efforts will provide information regar ding the contribution of electron transfer along DNA to formation of l ocally multiply damaged sites created in DNA by exposure to ionizing r adiation.