Fig. 5.
Operation of the negative feedback controller. a Structure and function of the negative feedback controller. In the absence of the circuit genes, repression of o-rRNA production is high, and so co-option of ribosomes to the orthogonal pool is low. Upon the introduction of a low demand circuit the o-ribosome pool is redistributed to express both circuit and controller genes. This reduces translation of the constitutively expressed controller due to resource competition, and as a result o-rRNA transcription increases. As circuit demand increases (here RFP transcription increases), increased resource competition results in a greater fall in controller translation. This reduces the repression of the o-rRNA production, allowing more co-option of ribosomes from the host ribosome pool. b Simulation showing the changing concentrations of the controller components in response to induction of RFP, which creates increased ribosomal demand. Note the narrow y-axis range. c Changing distribution of the translation complexes, c, in response to RFP induction of genes utilising o-ribosomes for translation. cF, controller mRNA-o-ribosome translation complex. d Protein output over time. Inset, coupling in the o-ribosome pool without controller. The induction rate of the o-rRNA was tuned so that both models produce the same protein concentration