Octaplex formation of d(GCGAAAGC) with the double A-quartet.

We reported that the sequence gcGA[X]1Agc adopts a specific structure to form several multiplexes. In the case of X=G, an octaplex formation occurs, in which the stacked double G-quartet stabilizes the architecture through potassium cation mediations. In the case of a mutant X=A, too, it has been found that the oligomers form an octaplex. The eight central A residues form a stacked double A-quartet, which is a first example of adenine associations. Several water molecules occupy the centre to stabilize the quartets, so that the octaplex seems to be swollen as compared with that of X=G. In any multiplex formations, the building block is a base-intercalated duplexes.