It is well established that the structure1,2 as well as the stability of the DNA duplex is affected by supercoiling. Supercoiled DNA has been shown to possess increased stability and is thus characterized by an elevated melting temperature as well as a broader melting transition. Thermal melting analysis has been the most widely used method for studying the structural and dynamic properties of complex DNA species. Here we report a remarkable attribute of supercoiled DNA, that the width of the melting transition of superhelical DNA does not depend appreciably on the relative stabilities of its A·T and G·C base pairs.
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