Proposed model depicting the mechanism of Ana2 recruitment to the site of procentriole assembly. (A) Schematics of Ana2, Plk4, and Sas4 showing structural and functional domains. Note that Plk4 initially exists in its autoinhibited form. Although these proteins homo-oligomerize, they are shown as monomers for simplicity. Only the C-terminal G-box domain of Sas4 is shown; it adopts an extended open β-sheet conformation. (B) During mitotic exit, unphosphorylated Ana2 (extended conformation) diffusing near a preprocentriole is weakly bound through its NT to one surface of the Sas4 G-box; substantial exchange of bound Ana2 with the cytoplasmic pool prevents sufficient accumulation at the preprocentriole to support centriole duplication. Plk4 also weakly binds the G-box through its PB1-PB2 cassette. (C) Ana2 binds and activates Plk4 by relieving its autoinhibition. In turn, active Plk4 phosphorylates the Ana2 NT, including S38, inducing Ana2 to fold. Subsequently, Plk4 phosphorylates the Ana2 STAN domain. During this step, Plk4 may be transferred from Sas4 to Ana2. (D) Phosphorylated NT and C-terminal domains of Ana2 bind one another and stabilize the folded conformation. Phospho-Ana2 binds tightly to the G-box through multiple contact sites. Tight binding to Sas4 allows Ana2 to accumulate on the preprocentriole, recruit Sas6, and promote centriole duplication. Further phosphorylation of the central domain in Ana2 causes Plk4 to release.