Bistable circuits without standard two-step cooperativity.

<p>(A) The exotic circuits. (B) Symmetrical circuits with two opposing pull-push motifs (upper) are not substantially bistable, while circuits with two destabilized pull-push motifs (lower) are. Simulations were without replication. (C) Left panel: Numbers of circuits among the 202 bistable E-opposite/R-out circuits with 0, 1 or 2 pull-push positive feedback pathways (left) or destabilized pull-push pathways towards either E1 or E2 shown according to whether the pathway is over the R-state, or the non-R state.