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 molecu le exists as a mixture of several multistranded structures whose stabi lities are dependent on added salt concentrations. There is one major conformation which can be selectively studied at low salt concentratio n and the NMR data indicate that this is a parallel stranded quadruple x with a novel A-tetrad at the 5'-end. The A-bases adopt the syn glyco sidic conformation as against the anti conformation adopted by the G-b ases in the three G-tetrads.