Folding and Topology of Quadruplexes

The formation of a quadruplex simply requires four guanine repeats to selfassociate. The simplest topology is formed by the self-association of four DNA strands in solution containing short guanine runs, for example 

More complex structures and topologies can form from strands containing two guanine repeats separated by non-guanine nucleotides, for example 

Intramolecular quadruplexes associate from the following general sequence. 

The folding topologies available to intramolecular quadruplexes are more varied and complex than those available to the intermolecular or bimolecular quadruplexes due to the additional linking nucleotides. Structural examples from X-ray and show just a few of the possible structures 

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