Tetracycline-controlled transactivator (tTAV) is a synthetic protein coding sequence based on a fusion of sequences from Escherichia coli and Herpes simplex virus (VP16 transcriptional activator). tTAV is under the control of its own binding site, tetO. In the absence of tetracycline, tTAV binds to tetO and drives expression of more tTAV, in a positive feedback loop. In the presence of tetracycline, tTAV binds tetracycline; this tetracycline-bound form does not bind tetO and so does not lead to expression of more tTAV. Consequently, this construct gives very high levels of expression of tTAV in the absence of tetracycline, but only low, basal expression in the presence of tetracycline. tTAV encodes a dominant trait that, when introduced into certain insects, causes death of the insect unless the antibiotic tetracycline is supplied.