T4 DNA topoisomerase: a new ATP-dependent enzyme essential for initiation of T4 bacteriophage DNA replication

Abstract
A novel ATP-dependent DNA topoisomerase which makes reversible double-strand breaks in the DNA double helix has been purified to near homogeneity from T4 bacteriophage-infected Escherichia coli cells. Genetic data suggest that this activity is essential for initiating T4 DNA replication forks in vivo.