Number of Tetrads

G-quadruplex structures can in principle form from any number of G-tetrad stacks. In general, the stability increases with increasing numbers of stacks. Single G-tetrads have only been reported in highly concentrated guanine solutions at mM concentrations, which are unlikely to be physiologically relevant. There are a few examples of double-stack quadruplexes, such as the thrombinbinding aptamer (TBA) and the sequences identified as responsible for the 

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It has been recognized that the stabilization by interactions with metal ions is essential in the formation of tetraplex structures. Based on the electrostatic potential analysis of the tetrads, a number of tetrads are suggested as the possible hosts of cations. The interaction between the cation and the tetrads remarkably alter the bonding patterns of the tetrads. 

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