Transcriptional activator TGV mediates dexamethasone-inducible and tetracycline-inactivatable gene expression

A chemically regulated gene expression system that can be switched on with dexamethasone and switched off with tetracycline was constructed. It is bas ed on a transcriptional activator (TGV) that consists of the Tn10 encoded T et repressor, the rat glucocorticoid receptor hormone binding domain and th e transcriptional activation domain of Herpes simplex virion protein VP16. When stably expressed in transgenic tobacco plants, it mediates dexamethaso ne-inducible transcription from a synthetic promoter (P-Top10) consisting o f seven fet operators upstream of a TATA-box. Tetracycline interferes with induction by negatively regulating the DNA-binding activity of the TetR moi ety of TGV. The boundaries of the expression window of the TGV-driven P-Top 10 reach from undetectable levels of the reporter enzyme beta-glucuronidase in the absence of dexamethasone to induced levels reaching 15-20% of the C auliflower Mosaic Virus 35S promoter (P-CaMV35S). By modifying the sequence of P-Top10, we generated a new target promoter (P-Tax) that is stably expr essed over several generations and that can be activated to levels comparab le to P-CaMV35S, while yielding only slightly elevated background activitie s.