Spectroscopic Evidence of Human Telomeric G-quadruplex

The structural interconversion between the G-quadruplex and duplex in vivo is an important\nsubject because it is believed that the formation of G-quadruplex structure depends on the denaturation\nof the duplex [1]. In the present study, we used human telomeric DNA duplex composed of\nGGG(TTAGGG)3/ CCC(TAACCC)3 as a model system to investigate its properties under near\nphysiological conditions by spectroscopic methods. Circular dichroism and fluorescence spectra\ndemonstrated that G-quadruplex structure can be formed from duplex at near physiological pH (pH\n7.4), salt concentration (150 mM K+), and temperature (37 oC) in the presence of molecular crowding\nagent PEG (40 %), whereas the G-quadruplex structure can not be formed at 25 oC in buffer\ncontaining 150 mM K+ in the presence of PEG. This work suggests that human telomeric\nG-quadruplex structure may be potentially formed from Watson-Crick duplex in vivo.