Fig. 1.

The TransActiVator (tTAV) feedback circuit. a Schematic of the tTAV system. b In the absence of tetracycline, basal levels of tTAV protein bind its own promoter at the TetO sites, thereby increasing tTAV protein production. This new protein binds the promoter and further increases expression. c In the presence of tetracycline, low levels of tTAV are sequestered and expression of tTAV mRNA remains at basal levels