NMR observation of a novel A-tetrad in a telomeric DNA segment in aqueous solution

NMR studies on the telomeric DNA segment d-AG 3 T show that the molecule exists as a mixture of several multistranded structures whose stabilities are dependent on added salt concentrations. There is one major conformation which can be selectively studied at low salt concentration and the NMR data indicate that this is a parallel stranded quadruplex with a novel A-tetrad at the 5' -end, The A-bases adopt the syn glycosidic conformation as against the anti conformation adopted by the G - bases in the three G - tetrads.