Recognition of GC base pairs by triplex forming oligonucleotides containing nucleosides derived from 2-aminopyridine.

We have attempted to alleviate the pH dependency of triplex recognition of guanine by using intermolecular triplexes containing 2-amino-5-(2-deoxy-d-ribofuranosyl)pyridine (AP) as an analogue of 2'-deoxycytidine (dC). We find that for the beta-anomer of AP, the complex between (AP)6T6and the target site G6A6*T6C6is stable, generating a clear DNase I footprint at oligonucleotide concentrations as low as 0.25 microM at pH 5.0, in contrast to 50 microM C6T6which has no effect on the cleavage pattern. This complex is still stable at pH 6.5 producing a footprint with 1 microM oligonucleotide. Oligonucleotides containing the alpha-anomer of AP are much less effective than the beta-anomer, though in some instances they are more stable than the unmodified oligonucleotides. The results of molecular dynamics studies on a range of AP-containing triplexes has rationalized the observed stability behaviour in terms of hydrogen-bonding behaviour.