Triple helix formation and the antigene strategy for sequence-specific control of gene expression

Specific gene expression involves the binding of natural ligands to the DNA base pairs. Among the compounds rationally designed for artificial regulat ion of gene expression, oligonucleotides can bind with a high specificity o f recognition to the major groove of double helical DNA by forming Hoogstee n type bonds with purine bases of the Watson-Crick base pairs, resulting in triple helix formation. Although the potential target sequences were origi nally restricted to polypurine polypyrimidine sequences, considerable effor ts were devoted to the extension of the repertoire by rational conception o f appropriate derivatives. Efficient tools based on triple helices were dev eloped for various biochemical applications such as the development of high ly specific artificial nucleases. The antigene strategy remains one of the most fascinating fields of tripler application to selectively control gene expression. Targeting of genomic sequences is now proved to be a valuable c oncept on a still limited number of studies; local mutagenesis is in this r espect an interesting application of tripler-forming oligonucleotides on ce ll cultures. Oligonucleotide penetration and compartmentalization in cells, stability to intracellular nucleases, accessibility of the target sequence s in the chromatin context, the residence time on the specific target are a ll limiting steps that require further optimization. The existence and the role of three-stranded DNA in vivo, its interaction with intracellular prot eins is worth investigating, especially relative to the regulation of gene transcription, recombination and repair processes. (C) 1999 Elsevier Scienc e B.V. All rights reserved.