The two domains of centrin have distinct basal body functions in Tetrahymena.

The basal body is a microtubule-organizing center responsible for organizing the cilium, a structure important for cell locomotion and sensing of the surrounding environment. A widely conserved basal body component is the Ca(2+)-binding protein centrin. Analyses of centrin function suggest a role in basal body assembly and stability; however, its molecular mechanisms remain unclear. Here we describe a mutagenic strategy to study the function and essential nature of the various structural features of Cen1 in the ciliate Tetrahymena. We find that the two domains of Cen1 are both essential, and examination of strains containing mutant CEN1 alleles indicates that there are two predominant basal body phenotypes: misorientation of newly assembled basal bodies and stability defects. The results also show that the two domains of Cen1 are able to bind Ca(2+) and that perturbation of Ca(2+) binding affects Cen1 function. In all, the data suggest that the two domains of Cen1 have distinct functions.