Component of the CYFIP1-EIF4E-FMR1 complex which binds to the mRNA cap and mediates translational repression. In the CYFIP1-EIF4E-FMR1 complex this subunit is an adapter between EIF4E and FMR1. Promotes the translation repression activity of FMR1 in brain probably by mediating its association with EIF4E and mRNA (By similarity). Regulates formation of membrane ruffles and lamellipodia. Plays a role in axon outgrowth. Binds to F-actin but not to RNA. Part of the WAVE complex that regulates actin filament reorganization via its interaction with the Arp2/3 complex. Actin remodeling activity is regulated by RAC1. Regulator of epithelial morphogenesis (By similarity). As component of the WAVE1 complex, required for BDNF-NTRK2 endocytic trafficking and signaling from early endosomes (By similarity). Component of the WAVE1 complex composed of ABI2, CYFIP1 or CYFIP2, BRK1, NCKAP1 and WASF1/WAVE1. Within the complex, a heterodimer containing NCKAP1 and CYFIP1 interacts with a heterotrimer formed by WAVE1, ABI2 and BRK1. Component of the CYFIP1-EIF4E-FMR1 complex which is composed of CYFIP, EIF4E and FMR1. Interacts with FMR1 but does not bind to related proteins FXR1 or FXR2. Interaction with EIF4E stimulates FMR1 binding. Component of the WAVE2 complex composed of ABI1, CYFIP1/SRA1, NCKAP1/NAP1 (NCKAP1l/HEM1 in hematopoietic cells) and WASF2/WAVE2. Interacts with the active GTP-bound form of RAC1. Interacts through its C-terminus with the C-terminus of DPYSL2/CRMP2 which is necessary for DPYSL2-induced axon outgrowth. Interacts with NYAP1, NYAP2 and MYO16. Interacts with TMEM108 (via N-terminus); the interaction associates TMEM108 with the WAVE1 complex (By similarity). Highly expressed in the perinuclear region (By similarity). Enriched in synaptosomes (By similarity). Also enriched in membrane ruffles and at the tips of lamellipodia (By similarity). Belongs to the CYFIP family.