8-oxo dG allows investigation of the structure and activity of oligonucleotides containing an 8-oxo mutation which is formed naturally when DNA is subjected to oxidative conditions or ionizing radiation. 5,6-Dihydro pyrimidines are naturally occurring compounds that are structural components of alanine transfer RNA. Dihydrouracil and the hydroxy pyrimidines are major base damage products formed by exposure of DNA to ionizing radiation.