The topology of DNA affects a number of major biological processes (1 -4 ). For example, processive enzymes, such as the RNA and DNA polymerases, have the capability of generating both positive and negative DNA supercoils during the process of transcription and replication, respectively. These supercoils must be relaxed in order for transcription and replication to continue unaffected, as outlined in preceding chapters. The DNA topoisomerases play the central role in relaxing this supercoiling (1 -4 ).