SUMMARYTo investigate the effects of heating rate on the DNA melting profile and to test the predictions of the theory of slow relaxation processes in DNA melting (1) concerning these effects, we obtained differential melting curves for the Bsp I Cl fragment of T7 DNA (1461 bp) and the Sma I-Eco RI fragment of Col El DNA (1291 bp) at heating Sates of 0.05 and 0.5 deg/min. At low ionic strength (0.02 M Na ) the heating rate has been shown to affect the position of the third peak in melting curve for Cl fragment.According to the melting maps (2), this peak corresponds to the unwinding of the section between the end of the molecule and Vhe region already melted.At high ionic strength (0.2 M Na ), when the melting of this DNA is reversible (3), the position of the peaks does not depend on the heating rate.In the case of the Col El DNA fragment the heating rate affects, as might be expected from the melting maps (4), only the last peak, as the melting of the last section is always nonequilibrium. The results of the study are in good qualitative agreement and in satisfactory quantitative agreement with the theoretical predictions (1).
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