Transcription repression-based logic evaluator. A) Conversion of a chemical into a repressor. When signal a is present, only repressor is expressed. Therefore–neglecting the other signals– pa n d 1 is not regulated and can lead to fluorescence production; vice versa when a is absent. This configuration requires two genes less than the siRNA-based one. B) Nuclear AND gates. C) Comparison of in silico simulations and in vivo measurements. Calculations are performed as in the RNAi-based circuit.