Abstract
NOVOBIOCIN and the related antibiotic coumermycin A1 (referred to as coumermycin) inhibit the supercoiling of circular double-stranded DNA catalysed by Escherichia coli DNA gyrase1. They also inhibit the replication of chromosomal DNA in E. coli cells2, and of circular double-stranded DNA in cell-free systems from E. coli3–6. The activity of DNA gyrase obtained from a coumermycin-resistant (cour) mutant and the replication of colicin El plasmid (Col El) DNA in a cell extract of the mutant are resistant to both drugs7. These results show that DNA gyrase is an essential component of these systems for the replication of the circular double-stranded DNA. It is interesting to examine whether DNA gyrase also has a role in replication of linear double-stranded DNA. The DNA of E. coli bacteriophage T7 is linear and double stranded8. Linear replicating molecules have been isolated from infected cells and it has been claimed that the phage DNA replicates as a linear form, at least in the first round of replication9. We show here that the replication of phage T7 DNA, including the first round, is inhibited by coumermycin.
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