May act as a link between RND2 signaling and regulation of the actin cytoskeleton (By similarity). 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 be required for the lysosomal retention of FASLG/FASL. Interacts specifically with GTP-bound RND2 and CDC42. Interacts with PDE6G and microtubules (By similarity). Homodimerizes, the dimers can polymerize end-to-end to form filamentous structures. Interacts with AKAP9, ARHGAP17, DAAM1, DIAPH1, DIAPH2, DNM1, DNM2, DNM3, FASLG/FASL, SNX2 and WASL/N-WASP. May interact with TNKS. Enriched in cortical regions coincident with F-actin. Also localizes to endocytic vesicles and lysosomes. Very highly expressed in the epithelial cells of the gastrointestinal tract, respiratory, reproductive and urinary systems. Also highly expressed in brown adipose tissue, cardiomyocytes, enteric ganglia and glucagon producing cells of the pancreas. Expressed in germ cells of the testis and all regions of the brain. 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. A chromosomal aberration involving FNBP1 is found in acute leukemias. Translocation t(9;11)(q34;q23) with KMT2A/MLL1. The relatively low incidence of the KMT2A/MLL1-FNBP1 fusion protein in acute leukemia may reflect the marginal capacity of this fusion protein to induce cellular transformation. Belongs to the FNBP1 family. Contaminating sequence. Potential poly-A sequence.