[Localization of melted regions in supercoiled DNA by means of chemical modification]

Diethyl pyrocarbonate was used as a probe in mapping early melting stages in supercoiled DNA. It was shown that in the process of early melting of pAO3 DNA two denatured regions (about 15 b.p.) arouse near the left and right boundaries of the cruciform structure. In course of further melting denatured regions appeared within AT-rich stretches and the cruciform structure itself disappeared.