Small GTPase required for ciliation. Activated in a guanine nucleotide exchange factor (GEF)-independent manner via its intrinsic GDP for GTP nucleotide exchange ability (PubMed:28625565). Involved in ciliary assembly by binding the intraflagellar transport (IFT) complex B from the large pool pre-docked at the base of the cilium and thus triggers its entry into the cilia (PubMed:28625565, PubMed:28428259). Interacts (in its GTP-bound form) with CEP19 (via residues 121-150); this interaction is required for its localization to the mother centriole and cilium basal body. Interacts (in its GTP-bound form) with the intraflagellar transport (IFT) complex B (via the IFT74-IFT81 heterodimer) (PubMed:28625565, PubMed:28428259). Binding to CEP19 and the IFT74-IFT81 heterodimer is mutually exclusive (PubMed:28428259). Localizes on the mother centriole. Localizes slightly apical to the subdistal appendage, but below the distal appendage. Expressed in the testis. Belongs to the small GTPase superfamily. Rab family.