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.