Plays a role in guidance and morphology of central and peripheral axons and in synaptic morphology. Also required for formation of cell membrane protrusions and for bristle development (By similarity). Interacts with Fmr1 and Rac1. Component of the WAVE complex composed of Hem/Kette, Scar/Wave and Sra-1/Cyfip where it binds through its C-terminus directly to Hem (By similarity). Accumulates in central axons and motor neuron terminals. Belongs to the CYFIP family.