Human telomeric G-quadruplex formed from duplex under near physiological conditions: spectroscopic evidence and kinetics.

The structural interconversion between the G-quadruplex and duplex in vivo is an important subject. In the present study, we used human telomeric DNA duplex composed of GGG(TTAGGG)(3)/CCC(TAACCC)(3) as a model system to investigate its properties under near physiological conditions by spectroscopic methods. Circular dichroism and fluorescence spectra demonstrated that G-quadruplex structure can be formed from duplex at near physiological pH (pH 7.4), salt concentration (150 mM K(+)), and temperature (37 degrees C) in the presence of molecular crowding agent PEG (400 g/l), whereas the G-quadruplex structure cannot be formed at 25 degrees C in buffer containing 150 mM K(+) in the presence of PEG. It is found that the formation rate of G-quadruplex structure depends on the temperature and the concentrations of both PEG and K(+). This work suggests that human telomeric G-quadruplex structure may be potentially formed from Watson-Crick duplex in vivo.