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. Detected predominantly at the plasma membrane of rod and cone photoreceptors. Not detected in the nucleus. Ubiquitous. Expressed in the rod and cone photoreceptors, extending from the tips of the outer segment (OS) through the inner segment (IS) and outer nuclear layer (ONL) and into the synaptic terminals of the outer plexiform layer (ONL). Also detected in the bipolar, horizontal and amacrine cells in the inner nuclear layer (INL), extending to the inner plexiform layer (IPL) and though the ganglion cell layer (GCL) and into the nerve fiber layer (NFL) (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 (Probable). Mutation of Cys-3 targets the protein to internal membranes. The disease is caused by variants affecting the gene represented in this entry. Belongs to the TBCC family. Retina International's Scientific Newsletter