Increase in synthesis and stability of sigma 32 on treatment with inhibitors of DNA gyrase in Escherichia coli.

We report here that in Escherichia coli, the anti-bacterial agent nalidixic acid induces transient stabilization and increased synthesis of sigma 32, accompanied by the induction of heat shock proteins (Dnak and GroEL proteins). The induction of heat shock proteins, increased synthesis of sigma 32, and stabilization of sigma 32 observed on treatment of wild-type cells with nalidixic acid were not observed in a nalA26 mutant, a strain that is resistant to nalidixic acid as the result of a mutation in the gyrA gene. Not only oxolinic acid, but also novobiocin, whose targets are the A and B subunits of DNA gyrase, respectively, also induced stabilization and increased synthesis of sigma 32. Thus, inhibition of the activity of DNA gyrase may cause stabilization and increased synthesis of sigma 32, resulting in turn in induction of heat shock proteins.