Spire and Formin 2 Synergize and Antagonize in Regulating Actin Assembly in Meiosis by a Ping-Pong Mechanism
Figure 3
Fmn2 binds with high affinity to Nt-Spire–capped barbed ends to restore filament growth.
(A) Barbed end growth from PA, initiated by 0.6 nM spectrin-actin seeds, 95% inhibited by Nt-Spire (93 nM, black line), with addition of FH1D-FH2 at indicated amounts in nM. Dashed lines, corresponding samples without seeds (same color coding). (B) Initial rates of barbed end growth from spectrin-actin seeds (0.6 nM; red symbols, from panel A) show a saturation behavior of Nt-Spire–bound barbed ends by FH1D-FH2. Open symbols, rate of spontaneous assembly under the same conditions, without seeds. (C) Seeded barbed end growth in the presence of 0.6 nM spectrin-actin seeds, Nt-Spire (93 nM) alone (black curve), and with addition of 25 nM FH1D-FH2 in the absence of inhibitors (red curve) and in the presence of KIND at 1.1 µM (light blue curve) or 3.5 µM (dark blue curve), in the presence of FSI at 1.1 µM (light green curve), and 2.2 µM (dark green curve).