Basal bodies organize cilia, which are microtubule-based cellular projections responsible for fluid flow and involved in signaling pathways. In Tetrahymena, cilia are arranged along cortical rows that propel the cells and into specialized structures within the oral apparatus that is used for feeding. Basal bodies are comprised of nine-triplet microtubules and hundreds of additional proteins. This structure, and many of the protein components in Tetrahymena are conserved in centrioles of vertebrate cells. We are interested in understanding the assembly of new basal bodies in hopes of revealing mechanisms conserved between basal bodies and centrioles. We have previously reported the basal body functions of the widely conserved component, centrin. Centrin binds a short repetitive sequence first found in the yeast centrosomal protein Sfi1. Human Sfi1 is found at centrioles. Centrioles also contain a related centrin-binding protein, Poc5. We have identified Tetrahymena orthologs of both Sfi1 and Poc5. These proteins are members of a large family of Tetrahymena proteins containing the centrin-binding motif, the Sfr family, on which we have previously reported. Many of the Sfr proteins localize asymmetrically around the basal body and play roles in basal body positioning, a role also demonstrated for centrin. As expected, TtSfi1 and TtPoc5 are found at basal bodies. Interestingly, both proteins only appear transiently at basal bodies during their assembly. Among the many Tetrahymena basal body components that have been examined, this behavior of transient localization is unique to TtSfi1 and TtPoc5. We believe that such localization is suggestive of important roles for these proteins in basal body assembly. TtPoc5 localizes to the basal body distal end, similar to hPoc5 in centrioles, while TtSfi1 localizes asymmetrically and is offset from the basal body microtubule scaffold. Preliminary data from a TtSfi1 macronuclear null strain suggests significant basal body defects. Micronuclear null strains for both TtSfi1 and TtPoc5 have been constructed and the basal body phenotypes of these strains will be examined.