Figure 7.
A proposed folding mechanism of eight tandem repeats of d(ccGA[G]4Agg). (a) A long chain is folded at the two linkers between the second and third repeats and between the sixth and seventh repeats. (b) Base-intercalated duplexes are formed between the anti-parallel strands. (c) The two parts are further folded; one is between the first and second repeats and between the third and fourth repeats, and the other is between the fifth and sixth repeats and between the seventh and eighth repeats, to form a quadruplex in each part. This folding pattern is similar to a Greek-key motif, which is well known in protein folding. (d) Finally the two quadruplexes are associated to form an octaplex with a double Greek-key motif.