Construction of a gyrA-gyrB-carrying plasmid overproducing functional DNA gyrase.

A plasmid carrying both gyrA and gyrB genes (pTS7) and a plasmid without the gyr gene (pTS4) were constructed. Introduction of pTS7 into the YK1100 (wild-type) cells resulted in an increase in the level of gyrA and gyrB mRNA by 5- to 6-fold over the level of the control transformant with pTS4. In the transformant cells carrying pTS7, the reporter plasmid pGP241, which is compatible with pTS plasmids, was significantly more highly negatively supercoiled than in the transformant with pTS4. The activity of DNA gyrase to supercoil the relaxed pGP241 DNA was 4-8 times higher with the S-30 extract from the transformant carrying pTS7 than with the extract from the transformant with pTS4.