The thermal denaturation of DNA: average length and composition of denatured areas

A spectral study of melting curves of DNA ranging from 73 to 32% AT indicates that the base ratio of sequences melting within DNA are a linear function of temperature. A study of partially denatured DNA by electron microscopy, reversible renaturation and fractionation on hydroxylapatite suggests that the melting curve of DNA represents the melting of sequences which average 3-4 million daltons in length. These sequences appear to be a combination of two areas, one which is high in AT and denatures in the first three-quarters of the melting curve, and one which is high in GC and denatures in the final quarter. The length of these sequences appears to vary between 1.5-6 million daltons.