RNAi-based logic evaluator. A) Conversion of a chemical into a siRNA. Following Rinaudo et at., signal a inhibits siRNA-a and promotes siRNA- expression. This double function is mimicked by requiring that this chemical binds and deactivates two different transcription factors. When a is present, only siRNA- is transcribed thus–neglecting other signals in the circuit– A N D2 mRNA is cleaved whereas A N D1 produces fluorescence; vice versa in absence of a. B) Cytoplasmic AND gates. C) Comparison of in silico simulations and in vivo measurements. For each truth table entry, we calculated the ratio between the corresponding fluorescent protein concentration and the minimal 1-output value (absolute values are shown in Additional file 1). This is the procedure followed by Rinaudo and co-authors (in their case, the lowest 1 concentration is at the entry “0010”). They, however, measured fluorescence.