In general, the GQs are polymorphic, can be built from single or multiple molecules, and can contain antiparallel, parallel strand, or mixed (hybrid) orientations, and these features result in distinct topological arrangements.
The modified GQs adopted the same type of antiparallel topology as the wild-type did, based on the CD spectra.
The probe minimally perturbed the GQ topology and stability and could distinguish the antiparallel, hybrid, and parallel topologies of DNA and RNA GQs from the corresponding duplexes.
The resulting two aptamers folded into the typical antiparallel chair-like GQ structures formed also by the native TBA in [K.sup.+] buffer (Figure 2).
The flexible abasic sites increased [T.sub.m] of the unmodified TBA GQ (49[degrees]C) by 6[degrees]C at each of the three positions and did not alter the antiparallel chair folding topology of the unmodified GQ.
The bisconjugated TBA analog could fold into the chair-like, antiparallel GQ structure in [K.sup.+], typical of the native TBA GQ, and retained its thrombin-binding properties as well.
The TBA and its analogs displayed positive peaks near 245 and 295 nm and a negative one near 265 nm, typical of the antiparallel GQ structures.
In most cases, the parallel GQs of any molecularity contain all anti nucleosides, and the antiparallel and hybrid architectures (Figure 2) comprise both types of natural nucleosides.
[64] described in 1994 that incorporation of [br.sup.8]dG into the 20-mer [([T.sub.3][G.sub.2]).sub.4], which folded into a monomolecular antiparallel chair-type GQ (Figure 2, 2), stabilized the [([T.sub.3][G.sub.2]).sub.4] by 5-6[degrees]C in the [T.sub.m] value when syn dGs were switched to [br.sup.8]dGs.
CD spectrum of [[T[[br.sup.8]G.bar]GGT].sub.4] showed, surprisingly, antiparallel characteristics and its thermal stability was much higher, by 13.3[degrees]C, than that of the native parallel tetramolecular scaffold.
Thermal stability of the two-tetrad antiparallel GQ increased when syn dGs were replaced and decreased when an anti dG was substituted by [m.sup.8]dG.
CD spectra of the three modified GQs in [Na.sup.+] looked hybrid types contrary to the wild-type's antiparallel spectrum (Figure 3).