Thermodynamics of tetraplex DNAs, (T2G4)n and (T4G4)n

The ends of eukaryotic chromosomes, termed telomeres, contain stretches of tandemly repeated guanine-rich sequences, such as (T2G4)n and (T4G4)n, along one strand. These sequences can form defined folded tetraplex structures in solution. Here we have systematically investigated the thermodynamic properties of a series of sequences, Tet n: (T2G4)n and Oxy n: (T4G4)n (n = 1, 2, 3, 4), in 10mM NaPi, 250mM NaCl, pH7.0, using differential scanning calorimetry (DSC). The melting process of all tetraplex DNAs is reversible. Tet n and Oxy n are similar in the dependence of melting temperature, Tm, and transition calorimetric enthalpy per strand, delta Hcal, on the number of the tandem sequence. The total delta Hcal value of Tet n is similar in magnitude to that of Oxy n, whereas the Tm value of the main fraction of Tet n is greater than that of Oxy n. These results suggest that Tet n and Oxy n form similar tetraplex DNA configuration, and the difference in Tm values between Tet n and Oxy n is attributed to the length of the T strings.