A chimeric transactivator comprises a transcription activation domain, a repressor protein DNA binding domain and the bacterial DNA gyrase B subunit. A target gene is operatively linked to operator DNA sequences recognized by the repressor binding domain. The addition of the antibiotic coumermycin results in a coumermycin-switched dimerization of the transactivator, which then binds to operator DNA sequences and activates transcription of the target gene. The addition of novobiocin switches off expression of the target gene by abolishing coumermycin-induced dimerization of the transactivator.
