Conformational Flexibility in DNA Structure as Revealed by Structural Studies of Drug Intercalation and Its Broader Implications in Understanding the Organization of DNA in Chromatin

Abstract

During the past few years there has been a growing awareness that conformational flexibility exists within double-helical DNA and that this flexibility is an important aspect in understanding its structure and function (Li and Crothers 1969; Pohl and Jovin 1972; Lang 1973; McGhee and von Hippel 1975a,b; Teitelbaum and Englander 1975a,b; Crick and Klug 1975; Sobell et al. 1976, 1977a,b). Thus, condensed forms of DNA have been observed by electron microscopy from ethanol-water mixtures; these forms can be produced by bending DNA to give different hierarchies of superhelical DNA structures (Lang 1973; Lang et al. 1976). Other conformational alterations in DNA and in DNA-like polymers have been produced by a variety of techniques under different conditions (Mahler et al. 1968; Pohl and Jovin 1972; Lerman 1974; Mercado and Tomasz 1977). At least one of these structures undergoes an allosteric conformational transition in the presence of ethidium bromide, as indicated by...