Fig. 2. Combining incoherent feedforward (IFF) and negative feedback (NF) loops is predicted to widen the copy number range with efficient dosage compensation.

a Schematic of the miRNA-based post-transcriptional IFF circuit. b The depletion of free RISC (gray trace) at high plasmid copy numbers abolishes dosage compensation by the IFF circuit (purple trace). c Schematic of the transcriptional NF circuit. d Incomplete repression by TetR results in a higher baseline transcription rate per plasmid (solid gray trace) that narrows the compensation range (leaky vs. ideal NF). Simulations were run with a doxycycline concentration that resulted in a wide compensation range of the NF circuit (1 ng/mL for both the ideal and leaky NF loops; see Supplementary Fig. 2). e Schematic of the Equalizer circuit, which combines transcriptional NF (green shaded area) with post-transcriptional IFF (purple shaded area). f Equalizer has the potential for compensating for a wider range of plasmid copy numbers than NF and IFF circuits alone. Simulated doxycycline concentration, 1 ng/mL.