This domain of about 280 residues is found in eukaryotes. There are two conserved sequence motifs: GFC and GLL. This family is also known as UPF0704. This domain is found in FAP206, a protein associated with cilia and flagella. In the ciliate Tetrahymena, the cilium has radial spokes, each of which is a macromolecular complex essential for motility. A triplet of three radial spokes, RS1, RS2, and RS3, is repeated every 96 nm along the doublet microtubule. Each spoke has a distinct base that docks to the doublet and is linked to different inner dynein arms. Knockout of the FAP206 gene results in slow cell motility and the 96-nm repeats lack RS2 and dynein c. FAP206 is probably part of the front prong and docks RS2 and dynein c to the microtubule.