THE TWISTED LIFE OF DNA IN THE CELL - BACTERIAL TOPOISOMERASES

DNA topoisomerases are essential to the cell for the regulation of DNA supercoiling levels and for chromosome decatenation. The proposed mec hanisms for these reactions are essentially the same, except that a ch ange in supercoiling is due to an intramolecular event, while decatena tion requires an intermolecular event, The characterized bacterial top oisomerases appear capable of both types of reaction in vitro. Four DN A topoisomerases have been identified in Escherichia coil. Topoisomera se I, gyrase, and topoisomerase IV normally appear to have distinct es sential functions within the cell. Gyrase and topoisomerase I are resp onsible for the regulation of DNA supercoiling. Both gyrase and topois omerase IV are necessary for chromosomal decatenation. Multiple topois omerases with distinct functions may give the cell more precise contro l over DNA topology by allowing tighter regulation of the principal en zymatic activities of these different proteins.