Effect of cationic comb-type copolymer on quadruplex folding of human telomeric DNA.

Cationic comb-type copolymer (CCC) consisting of a polycationic backbone and abundant graft water-soluble chains exhibited considerable stabilization effect on DNA hybrids, such as double- and triple-stranded DNAs. Here, we describe the effect of CCC on antiparallel G-quadruplex folding of human telomeric DNA, d(GGGTTA)(n) in the presence of sodium ions. CCC did not significantly alter the circular dichroism (CD) spectra of d((GGGTTA)(3)GGG) and d((GGGTTA)(7)GGG) indicating that the CCC did not influence the antiparallel folding of the telomeric repeats. Hence, the ionic interaction of CCC with the DNA sequence did not interfere with specific interaction of the DNA with sodium ions to form G-quartets. Interestingly, CCC did not change the melting temperature of the d((GGGTTA)(3)GGG) suggesting negligible stabilizing effect of CCC on the antiparallel quadruplex structure.