Cloning of the DNA gyrase genes under tac promoter control: overproduction of the gyrase A and B proteins.

The construction of plasmids which over-produce the Escherichia coli DNA gyrase A and B proteins (GyrA and GyrB) is described. Both plasmids are based on the pTTQ vectors of Stark [Gene 51 (1987) 255-267] and contain either the gyrA or gyrB gene under the tight control of the hybrid tac promoter. Expression of the gyrase genes is shown to be repressed in the absence of the inducer IPTG, but in its presence, strains containing these plasmids synthesise the A and B proteins to about 40% of soluble cell protein.