DNA Gyrase and DNA Supercoiling

Abstract

Double-stranded circular DNA, when isolated from cells or virions, is generally found to be supercoiled. The direction of supercoiling is always the same; the DNA strands are wound around each other too few times to permit a relaxed conformation to exist. This DNA structure is termed underwound, or negatively supercoiled. Until recently it has not been possible to determine how this supercoiling is generated. Two general classes of models, which may be termed passive and active, have been discussed.