Temperature-induced perturbations in the circular dichroic spectrum of the synthetic polymer poly[d(G-C)]

The effect of increasing temperature on the double-helical synthetic DNA polymer poly[d(G-C)] with alternating base sequence, was studied by ultraviolet absorbance and circular dichroic techniques. While a cooperative hyperchromic effect was noticed in the ultraviolet absorbance spectrum above a temperature of 70 degrees C, an inversion of the circular dichroic spectrum was observed at a similar temperature range. On cooling to room temperature, the spectrum was reversed to the initial one. These observations, first reported here, are tentatively attributed to a conformational change of the polymer, from the right-handed double helix to the left-handed single strands, prior to complete denaturation.