Covalent crosslinks introduced via a triple helix-forming oligonucleotide coupled to psoralen are inefficiently repaired

Triple helix-forming oligonucleotides (TFOs) represent potentially powerful tools to artificially modulate gene activity. In particular, they can be u sed to specifically introduce a lesion into a selected target sequence: int erstrand crosslinks and monoadducts can be introduced via TFOs coupled to p soralen, The efficiency of these strategies depends on the cell ability to repair these lesions, an issue which is still controversial. Here we show, using psoralen-coupled TFOs and the yeast as a convenient cellular test sys tem, that interstrand crosslinks ape quantitatively poorly repaired, result ing in an efficient modification of target gene activity. In addition, thes e lesions result in the introduction of mutations in a high proportion of c ells. We show that these mutations are generated by the Error-Prone Repair pathway, alone or in combination with Nucleotide Excision Repair. Taken tog ether, these results suggest that TFOs coupled to psoralen could be used to inactivate a gene with significant efficiency.