Triple helix formation with oligodeoxyribonucleotides containing 8-oxo-2'-deoxyadenosine and 2'-modified nucleoside derivatives.

The ability of homopyrimidine oligonucleotides containing 8-oxo-2'-deoxyadenosine (dAOH) and/or 2'-methoxyuridine (Um) or 2'-fluorouridine (Uf) to form stable, triple helical structures with the sequences containing the recognition site for the class II-S restriction enzyme, Ksp632-I, was studied as a function of pH. The 8-oxo-2'-deoxyadenosine substituted oligomers were shown to bind within the physiological pH range in a pH-independent fashion, without a compromise specificity. On the other hand, the oligonucleotides containing 2'-modified nucleosides (Uf ,Um, dAOH-Um, and dAOH-Uf) bind in a pH-dependent mannerto the target duplex.