Acts as a GTPase-activating protein (GAP) involved in trafficking between the Golgi and the ciliary membrane. Involved in localization of proteins, such as NPHP3, to the cilium membrane by inducing hydrolysis of GTP ARL3, leading to the release of UNC119 (or UNC119B). Acts as a GTPase-activating protein (GAP) for tubulin in concert with tubulin-specific chaperone C, but does not enhance tubulin heterodimerization. Acts as guanine nucleotide dissociation inhibitor towards ADP-ribosylation factor-like proteins. Found in a complex with ARL3, RP2 and UNC119 (or UNC119B); RP2 induces hydrolysis of GTP ARL3 in the complex, leading to the release of UNC119 (or UNC119B). Interacts with ARL3; interaction is direct and stimulated with the activated GTP-bound form of ARL3 (By similarity). Detected predominantly at the plasma membrane of rod and cone photoreceptors. Not detected in the nucleus. Retina (at protein level). Myristoylated on Gly-2; which may be required for membrane targeting. Palmitoylated on Cys-3; which may be required for plasma membrane targeting. Belongs to the TBCC family.