Measurement of the radiosensitivity of a radiation-induced adenine defect in a single stranded DNA chain.

To determine the radiation sensitivity of an adenine defect inside the DNA chain, an oligonucleotide bearing 7,8-dihydro-8-oxoadenine was chemically synthesized by the phosphoramidite method. This damaged oligonucleotide 32P-labelled at one end was gamma irradiated in an aerated aqueous solution, and heated with piperidine. The fragments obtained were separated by polyacrylamide sequencing gel electrophoresis, according to their chain lengths. Mean radiosensitivity coefficients for the four natural nucleotides and the relative radiation sensitivity of 7,8-dihydro-8-oxoadenine leading to chain rupture in alkaline medium, could be obtained from the band intensities by computer calculation. An unexpectedly high value was obtained for the damaged adenine residue. Determinations were performed for different doses of irradiation.