An Escherichia coli mutant thermosensitive in the B subunit of DNA gyrase: effect on the structure and replication of the colicin E1 plasmid in vitro.

An E. coli strain which carries a mutation conferring clorobiocin resistance and temperature sensitivity for growth has recently been described and evidence has been presented suggesting that the mutation is located in the gyrB gene (Orr et al. 1979). The replication of the ColE1 plasmid was analysed in cell-free extracts from this thermosensitive strain. These extracts were totally deficient in the replication of exogenous plasmid DNA and were unable to maintain the superhelical structure of the plasmid DNA. Both defects could be fully complemented by addition of purified gyrB protein.