125I decay in synthetic oligodeoxynucleotides

The availability of synthetic oligodeoxynucleotides provides the opportunity to study the effects of 125I in DNA with added precision and detail, compared to an earlier study (Martin and Haseltine, Science 214, 296, 1981). The authors have designed a template/primer system which enables incorporation of 125IdC into a defined location in a 31mer. The main advantage of this approach is that relatively large amounts (a few μCi) of DNA with both 32P and 125I can be produced quite easily. Consequently, when 125I-induced DNA damage is analyzed on DNA sequencing gels, the distribution of 32P-labeled cleavage products can be determined more accurately, following accumulation of decay events under various conditions (e.g. temperature, buffer components, free radical scavengers). The results of preliminary experiments suggest that the yield of DNA strand breaks per decay approaches one, at least for the 125I labeled strand. Extension of this experimental approach will also enable investigation of the nature of the terminii (e.g. phophoryl-versus phophorylglycollate) at either side of 125I decay-induced DNA strand breaks. The question of energy migration is also being investigated in the oligodeoxynucleotide system, by studying the effects of inclusion of BrUdR nucleotides at various distances from the 125IdC