Probably involved in membrane protein trafficking at the base of the ciliary organelle. May function in cilia biogenesis. Isoform 2 is required for proper retinal function and organization. Expressed in brain, heart and eye. Isoform 2 is expressed only in the retina. Expressed throughout all the development stages. Isoform 2 is not expressed until 48 hours post fertilization. Results in the cardinal features of Bardet-Biedl syndrome in zebrafish, including defects to the ciliated Kupffer's vesicle and delayed retrograde melanosome transport. Isoform 2 defects does not result in Kupffer vesicle or melanosome transport defects, but rather leads to impaired visual function and mislocalization of the photopigment green cone opsin. Isoform 2, but not isoform 1, is sufficient to rescue both the vision defect as well as green opsin localization in the retina. Belongs to the small GTPase superfamily. Arf family.