To Study The Quality Of G-qudruplex And I-motif

It is well reported that human telomeric DNA sequence [AGGG(TTAGGG)3] can form a well-defined quadruplex structure with the hydrogen bond between guanine bases in the appearance of K+ and Na+. It was reported that the formation and stability of the structure is meaningful for both gene regulation and apoptosis. In this study, we have replaced guanine bases in this sequence with T, A and C at different position respectively. Their ability to form G-quadruplex as well as G-quadruplex stability has been studied by circular dichroism (CD) spectroscopy and UV-Vis spectroscopy. Results show that the replacement of guanine bases in the middle of three stacking quartets brings the biggest influence on the stability of formed G-quadruplex. Data also show that potassium ions bring more stability than sodium ions to the formed G-quadruplex in most cases. It is very interesting to find that, when guanine base is replaced by cytosine or adenine at specific sites, the formed structure has comparable or even higher stability as the original sequence.