Basal bodies organize cilia that are responsible for both mechanical beating and sensation. Nascent basal body assembly follows a series of well characterized morphological events; however, the proteins and their assembly dynamics for new basal body formation and function are not well understood. High-resolution light and electron microscopy studies were performed in Tetrahymena thermophila to determine how proteins assemble into the structure. We identify unique dynamics at basal bodies for each of the four proteins analyzed (α-tubulin, Spag6, centrin, and Sas6a). α-Tubulin incorporates only during new basal body assembly, Spag6 continuously exchanges at basal bodies, and centrin and Sas6a exhibit both of these patterns. Centrin loads and exchanges at the basal body distal end and stably incorporates during new basal body assembly at the nascent site of assembly and the microtubule cylinder. Conversely, both dynamic and stable populations of Sas6a are found only at a single site, the cartwheel. The bimodal dynamics found for centrin and Sas6a reveal unique protein assembly mechanisms at basal bodies that may reflect novel functions for these important basal body and centriolar proteins.
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