Fusions of the Escherichia coli gyrA and gyrB control regions to the galactokinase gene are inducible by coumermycin treatment.

We have previously shown that the genes encoding the two subunits of Escherichia coli DNA gyrase are regulated in a manner which is dependent on DNA conformation. When the DNA encoding the gyrA and gyrB genes is relaxed, both genes are expressed at a high level; in negatively supercoiled DNA they are expressed at a low level. In this paper we describe fusions of both the gyrA and gyrB 5' sequences to the E. coli galactokinase gene. In such fusions we found that galactokinase can be induced by treating the cells with coumermycin A1, an inhibitor of DNA gyrase. Our results suggest that the regulation occurs at the transcriptional level and that only a small region of DNA is necessary for coumermycin-induced gene expression.