Required to coordinate membrane tubulation with reorganization of the actin cytoskeleton during the late stage of clathrin-mediated endocytosis. Binds to lipids such as phosphatidylinositol 4,5-bisphosphate and phosphatidylserine and promotes membrane invagination and the formation of tubules. Also enhances actin polymerization via the recruitment of WASL/N-WASP, which in turn activates the Arp2/3 complex. Actin polymerization may promote the fission of membrane tubules to form endocytic vesicles. May act as a link between RND2 signaling and regulation of the actin cytoskeleton. May be required for the lysosomal retention of FASLG/FASL (By similarity). Homodimerizes, the dimers can polymerize end-to-end to form filamentous structures. Interacts specifically with GTP-bound RND2 and CDC42. Interacts with AKAP9, ARHGAP17, DAAM1, DIAPH1, DIAPH2, DNM1, DNM2, DNM3, FASLG/FASL, microtubules, PDE6G, SNX2 and WASL/N-WASP. May interact with TNKS (By similarity). Enriched in cortical regions coincident with F-actin. Also localizes to endocytic vesicles and lysosomes. Expressed in brain and testis. The F-BAR domain binds the phospholipid membrane with its concave surface. The end-to-end polymerization of dimers of these domains provides a curved surface that fits best membranes with around 600 A diameter, and may drive tubulation (By similarity). Belongs to the FNBP1 family.