SEQUENCE-SPECIFIC DNA BREAKS PRODUCED BY TRIPLEX-DIRECTED DECAY OF I-125

Tripler forming oligonucleotides (TFO) labeled with Auger emitters cou ld be ideal vehicles to deliver radioactive-decay energy to specific D NA sequences, causing DNA breaks and, subsequently, inactivation of th ese sequences. To demonstrate this approach we labeled with I-125 (two I-125 per molecule on average) a purine-rich 38-mer which forms a sta ble tripler with a polypurine polypyrimidine stretch in the human HPRT gene. Decay of I-125 in the bound TFO was shown to cause sequence-spe cific double strand breaks (DSB) in the target HPRT sequence cloned in to plasmid DNA. No sequence-specific breaks were observed if (125)-lab eled TFO were not bound to the plasmid DNA, After 60 days of decay acc umulation (one I-125 half-life) approximately a quarter of all plasmid molecules contained sequence-specific DSB, corresponding to 0.3 site- specific DSB per decay. Sequencing gel analysis shows that the DNA bre aks are distributed within a few bases of the maxima at those bases op posite to the positions of I-125 in the TFO.