SEQUENCE-SPECIFIC DNA DOUBLE-STRAND BREAKS INDUCED BY TRIPLEX FORMING I-125 LABELED OLIGONUCLEOTIDES

A triplex-forming oligonucleotide (TFO) complementary to the polypurine-polypyrimidine region of the nef gene of the Human Immunodeficiency Virus (HIV) was labeled with I-125 at the C5 position of a single deoxycytosine residue. Labeled TFO was incubated with a plasmid containing a fragment of the nef gene. Decay of I-125 was found to cause double-strand breaks (DSB) within the nef gene upon tripler formation in a sequence specific manner. No DSB were detected after incubation at ionic conditions preventing tripler formation or when TFO was labeled with P-32 instead of I-125. Mapping DSB sites with single base resolution showed that they are distributed within 10 bp of a maximum located exactly opposite the position of the [I-125] IdC in the TFO. We estimate that on average the amount of DSB produced per decay is close to one.