Figure 3.

PLK4 Symmetry Breaking Requires a Balance of Protein Expression and Degradation and Positive Feedback Based on the PLK4 Kinase Activity

Domain of symmetry breaking is shown by color in all panels.

(A) Symmetry breaking occurs at the optimal combination of protein expression and degradation rates. Respective PLK4 and STIL parameters were kept equal.

(B) Symmetry breaking requires autocatalytic cross-phosphorylation of both PLK4 and STIL.

(C) Cross-phosphorylation and retention of phosphorylated PLK4-STIL complexes are the two parts of the dual PLK4-activity-based feedback required for procentriole formation. x axis represents the ratio of the off rate $k_{off}^{\ast }$for the PLK4-STIL complexes phosphorylated on STIL (PS*, P*S*) to the off rate k_off of P, PS, and P*S. Cross-phosphorylation rates of STIL and PLK4 were kept equal.