DNA triplex can be formed by interaction of double-stranded sequence-specific single-stranded DNA oligonucleotides called TFO. There are many potential uses triple-stranded structures induction strategies for these molecules. They allow specific blocking sequence replication, and regulation of gene expression by inhibiting transcription. Particularly promising, due to the potential for use in gene therapy is the ability to introduce mutations TFO into the genomic DNA, and the induction of homologous recombination.