The ttgTA entry in FlyBase represents an artificial transcriptional activator ('driver') that includes the DNA-binding domain from the ttgR gene of Pseudomonas putida and a transcriptional activation domain from the Herpes simplex virus Type 1 VP16 gene. The ttgR DNA-binding domain binds specifically to the ttgO DNA sequence, and thus ttgO and ttgTA form a binary expression system that can be used to control the spatial and temporal expression of a gene of interest: a transgene or modified endogenous locus carrying the target gene of interest downstream of ttgO sequences is combined with a second transgene or modified endogenous locus encoding the ttgTA driver. The activity of the ttgTA driver can potentially be suppressed by phloretin (a specific ligand of ttgR): upon binding to phloretin it is expected that ttgTA will undergo a conformational change preventing it from binding the ttgO sequence, thus reducing or preventing its ability to induce transcription (PMID:19549857). The exact sequence of the driver may differ depending on the particular transgene or modified endogenous locus being used. In particular, the number of VP16 activation domains present may vary, and/or the VP16 activation domains may contain mutations that alter the strength of transcriptional activation.