A novel parallel-stranded DNA helix with non canonical A-T and G-C base pairing in synthetic dodecamers

Interaction between two synthetic deoxyoligonucleotide dodecamers of the sa me sequence (AGATCTAGATCT) but with reverse polarity at pH 5.2 tvas studied by UV and CD spectroscopy. UV mixing curve demonstrates formation of 1 : 1 complex between the two dodecamers, which can only be a parallel-stranded DNA (PS-DNA) structure. UV melting curve and CD spectral data are consisten t with this view. The PS-DNA possibly form at pH 5.2 by reverse Watson-Cric k A-T base pairs and reverse Hoogsteen G-C+ base pairs in the same DNA heli x. This is the first report of such a novel structure.