Fbp17 promotes WASP-mediated actin polymerization. (A) Co-IP of GFP-WASP and Teep1-GFP with RFP-Fbp17. IP was performed with RFP-trap and samples were probed with GFP or RFP antibody. (B) Co-IP of RFP-Fbp17, -Fbp17^ΔSH3, or -Fbp17^SH3 with GFP-WASP. IP was performed with RFP-trap and samples were probed with GFP or RFP antibody. (C) Pull-down of GFP-WASP from cell lysate with GST or GST-SH3 immobilized on beads. Samples were probed with GFP antibody. The protein-transferred membrane was stained with Coomassie Brilliant Blue (CBB) to show purified GST and GST-SH3. (D) Pull-down of GFP-WASP from cell lysate with GST-SH3 or MBP-SH3 immobilized on beads. Samples were probed with GFP antibody. The protein-transferred membrane was stained with Ponceau S to show purified GST and MBP fusion proteins. (E) Localization of GxcM-RFP and GFP-WASP in WT and fbp17⁻ cells. Scale bar, 5 μm. (F) GST-SH3, but not SH3 or GST-Fbp17, promotes WASP- and Arp2/3-mediated actin polymerization in pyrene assays. (G) GST-SH3 promotes WASP- and Arp2/3-dependent actin polymerization in a concentration-dependent manner in pyrene assays. The VCA domain of WASP purified as a GST fusion was included as a control. Source data are available for this figure: SourceData F6.