Fig. 3. Proposed origin of bistability in the CRISPRi TS.

a Binding configurations of two dCas9/sgRNA variants (colors). We assume a specific binding site for one variant (box) and unspecific binding during screening of PAM sequences for both variants. Arrows: binding/unbinding reactions. b Bifurcation diagram for the mathematical model with specific and unspecific dCas9/sgRNA binding (biologically constrained parameters; see Supplementary Fig. 12 and Supplementary Table 4). Solid (dashed) lines: stable (unstable) steady states; red stars: tangent bifurcations; gray: bistability region. Note that sgRNA-1 (abbreviated sg1) and sgRNA-2 (sg2) in the model represent two generic sgRNAs, and not necessarily the specific sequences labeled as sgRNA-1 and sgRNA-2 in the experimental parts of this work.