The TetR regulon and pYR cell based repression-induction system. A) The tetracycline resistance conferring tetR-tetA regulon. The repressor gene, tetR, is depicted as a dark gray arrow and the resistance gene, tetA, as a light gray arrow. TetR regulates the transcription of tetA and its own gene by binding operators O1 and O2. The binding of TetR to the operator sequences is inhibited by interaction with Tc. B) Plasmid map of pYR
and the scheme of the cell based repression-induction system. TetR expressed from the pBAD promoter on pYR
represses trancription of the lux genes on the same plasmid. Upon addition of Tc, TetR is induced, the lux genes are transcribed, and luminescence is emitted from the cells. If active TetX enzyme is produced from pET
, then the effective concentration of Tc is reduced by the activity of the enzyme and the transcription level of the lux genes is also reduced, resulting in decreased luminescence. The box represents the E. coli cell membrane.