Tetrahymena thermophila contains a conventional γ-tubulin that is differentially required for the maintenance of different microtubule-organizing centers

The gene (GTU1) encoding Tetrahymena thermophila γ-tubulin was cloned and analyzed. GTU1 is a single-copy, essential gene encoding a conventional γ-tubulin. HA-tagged GTU1p localizes to four microtubule-organizing centers (MTOCs) in vegetative cells: basal bodies (BBs), macronuclear envelopes, micronuclear envelopes, and contractile vacuole pores. γ-Tubulin function was studied by placing the GTU1 gene under control of an inducible–repressible promoter. Overexpression of GTU1 had no detectable effect on cell growth or morphology. Depletion of γ-tubulin resulted in marked changes in cell morphology and in MT bundling. MTOCs showed different sensitivities to γ-tubulin depletion, with BBs being the most sensitive. γ-Tubulin was required not only for the formation of new BBs but also for maintenance of mature BBs. BBs disappeared in stages, first losing γ-tubulin and then centrin and glutamylated tubulin. When GTU1 expression was reinduced in depleted cells, BBs reformed rapidly, and the normal, highly...