Acts as a GTPase-activating protein (GAP) involved in trafficking between the Golgi and the ciliary membrane (By similarity). Acts as a GTPase-activating protein (GAP) for tubulin in concert with tubulin-specific chaperone C, but does not enhance tubulin heterodimerization (By similarity). In the retina, required for maintenance of rod and cone photoreceptor cells (PubMed:26034134). May have a role in normal retinal localization of the transducins GNB1 and GNAT1, and the rhodopsin kinase GRK1 (PubMed:26034134). In the retina, detected in both rod and cone photoreceptors (at protein level) (PubMed:21282572, PubMed:26034134). Has strongest expression in the retinal outer nuclear layer (ONL) and weaker expression in the outer plexiform layer (OPL) and inner plexiform layer (IPL) (at protein level) (PubMed:26034134). Expressed in all tissues tested (PubMed:21282572). Expressed throughout development. Myristoylated on Gly-2; which may be required for membrane targeting. Palmitoylated on Cys-3; which may be required for plasma membrane targeting. Viable and fertile. Early retinal development appears to be grossly normal. Outer segments of rod and cone photoreceptors show progressive degeneration from 2 months of age, with rod cells more severely affected in the early stages. Belongs to the TBCC family. Contaminating sequence. Sequence of unknown origin at the N terminus.