Figure 5.

XOR gates based on simplified designs (Marchisio and Stelling, 2014). The latest version of the algorithm for the automatic design of bacterial gene digital circuit allows using inducers and corepressors as inputs for both POS and SOP circuits. Furthermore, two new interactions are taken into account: inducers binding repressors and corepressors binding activators. In both cases, the chemical inactivates its target protein. The circuits here shown take as inputs the inducer a, which activates a riboswitch/ribozyme, and the corepressor b, which inhibits an activator (A^a). NOT(a) is an active repressor (R^a); NOT(b) a small RNA (l, which means lock since, by annealing to the mRNA, prevents ribosome binding and translation initiation). (A) POS solution is still organized in three layers of gates and Pools. The corresponding Boolean formula has been rearranged as: $NOT\left(\left(\overline{a}\wedge \overline{b}\right)\vee \left(a\wedge b\right)\right).$ (B) SOP solution is designed according to the distributed output architecture. This implies a reduction in the complexity score with respect to the corresponding POS configuration.