Stabilisation of TG- and AG-containing antiparallel DNA triplexes by tripler-binding ligands

We have used DNase I footprinting to examine the interaction of several tri pler-binding ligands with antiparallel TG- and AG-containing triplexes. We find that although a 17mer TG-containing oligonucleotide on its own fails t o produce a footprint at concentrations as high as 30 CIM, this interaction can be stabilised by several ligands. Within a series of disubstituted ami doanthraquinones we find that the 2,7- regioisomer affords the best stabili sation of this TG tripler, though the 1,8- isomer also stabilises this inte raction to some extent. By contrast the 1,5- and 2,6- regioisomers show no interaction with TG triplexes. Similar studies with a 13mer AG-containing o ligonucleotide show the opposite pattern of stabilisation: the 2,6- and 1,5 - isomers stabilise this tripler, but the 2,7- and 1,8-compounds do not. Th e polycyclic compound BePI strongly stabilises TG- but not AG-containing tr iplexes, while a substituted naphthylquinoline interacts with both antipara llel tripler motifs.