TARGETED GENE KNOCKOUT MEDIATED BY TRIPLE-HELIX FORMING OLIGONUCLEOTIDES

Triple helix forming oligonucleotides (TFOs) recognize and bind sequen ces in duplex DNA and have received considerable attention because of their potential for targeting specific genomic sites(1-3). TFOs can de liver DNA reactive reagents to specific sequences in purified chromoso mal DNA (ref. 4) and nuclei(5). However, chromosome targeting in viabl e cells has not been demonstrated, and in vitro experiments indicate t hat chromatin structure is incompatible with tripler formation(6-8) We have prepared modified TFOs, linked to the DNA-crosslinking reagent p soralen. directed at a site in the Hprt gene. We show that stable Hprt -deficient clones can be recovered following introduction of the TFOs into viable cells and photoactivation of the psoralen. Analysis of 282 clones indicated that 85% contained mutations in the tripler target r egion. We observed mainly deletions and some insertions. These data in dicate that appropriately constructed TFOs can find chromosomal target s, and suggest that the chromatin structure in the target region is mo re dynamic than predicted by the in vitro experiments.