Quadruplex formation by a guanine-rich PNA oligomer

A guanine-rich PNA dodecamer having the sequence H-G(4)T(4)G(4)-Lys-NH2 (G(4)-PNA) hybridizes with a DNA dodecamer of homologous sequence to form a four-stranded quadruplex (Datta, B.; Schmitt, C.; Armitage, B. A. J. Am. Chem. Soc. 2003, 125, 4111-4118). This report describes quadruplex formation by the PNA alone. UV melting curves and fluorescence resonance energy transfer experiments reveal formation of a multistrancled structure stabilized by guanine tetrads. The ion dependency of these structures is analogous to that reported for DNA quadruplexes. Electrospray ionization mass spectrometry indicates that both dimeric and tetrameric quadruplexes are formed by G(4)-PNA, with the dimeric form being preferred. These results have implications for the use of G-rich PNA for homologous hybridization to G-rich targets in chromosomal DNA and suggest additional applications in assembling quadruplex structures within lipid bilayer environments.