DNA Supercoiling and Its Effects on DNA Structure and Function

Abstract

It was 17 years ago that Vinograd and his associates first deduced the supercoiled nature of the small circular DNA of polyoma virus. In a series of pioneering papers, the structural basis and consequences of DNA supercoiling were expounded (Vinograd et al. 1965, 1968; Vinograd and Lebowitz 1966; Bauer and Vinograd 1968). The basic points can be summarized as follows: (1) Supercoiling results when the two complementary strands in a duplex DNA ring are underwound (negatively supercoiled) or overwound (positively supercoiled). DNA supercoiling is analogous to the coiling of a torsionally unbalanced multistranded rope in space. The underwinding or overwinding of the strands is relative to the number of times the strands are intertwined in the same DNA under no torsional constraint. (2) Supercoiling is associated with an unfavorable free energy. Thus, any process that reduces the degree of supercoiling occurs more readily in a supercoiled DNA than in a...