The construction of oligonucleotides containing a modified nucleoside at a predefined site has provided new insights into the mechanisms of DNA repair and mutagenesis. 1 Organic chemists have played a key role by synthesizing nucleosides damaged by UV and ionizing radiation, chemical carcinogens, and chemotherapeutic agents. 2 Further incorporation of these modified nucleosides into oligonucleotides has enabled the direct study of ...