Table 1. Synthetic circuit size comparison.
| Publication | No. of gates/parts | No. of connections | No. of inputs | Circuit complexity (gates2+connections2)1/2 | Functionally complete parts? | Medium |
|---|---|---|---|---|---|---|
| Cascade circuit | 7 | 6 | 1 | 9.22 | Yes | S. cerevisiae |
| Nielsen et al.22 | 7 | 6 | 3 | 9.22 | Yes | E. coli |
| Qian et al.70 | 6 | 5 | 4 | 7.81 | Yes | In vitro |
| XOR circuit | 5 | 4 | 2 | 6.40 | Yes | S. cerevisiae |
| Xie et al.11 | 5 | 4 | 6 | 6.40 | No | Mammalian |
| Auslander et al.71 | 5 | 4 | 2 | 6.40 | No | Mammalian |
| Regot et al.72 | 5 | 3 | 2 | 5.83 | Yes | Multicellular S. cerevisiae |
| Nissim et al.33 | 5 | 3 | 1 | 5.83 | No | Mammalian |
| Stanton et al.19 | 4 | 3 | 2 | 5 | Yes | E. coli |
| Nielsen et al.18 | 3 | 2 | 2 | 3.61 | Yes | E. coli |
| Kiani et al.20 | 2 | 2 | 1 | 2.83 | No | Mammalian |
The best method for quantifying the size of synthetic biological circuits is an open question. Here we took the largest synthetic circuits constructed in recent publications and compared them with the two largest circuits from this paper. We separated the inputs to the circuits from internal components. We also counted the number of connections between the internal components. By our definition, a ‘part' is a molecular species that carries information necessary for the internal function of the circuit (as opposed to a helper protein such as cas9). A ‘connection' is a molecular interaction between parts that propagates information within the circuit.