HUMAN GAMMA-TUBULIN FUNCTIONS IN FISSION YEAST

gamma-Tubulin is a phylogenetically conserved component of microtubule-organizing centers that is essential for viability and microtubule function. To examine the functional conservation of gamma-tubulin, we have tested the ability of human gamma-tubulin to function in the fission yeast Schizosaccharomyces pombe. We have found that expression of a human gamma-tubulin cDNA restores viability and a near-normal growth rate to cells of S. pombe lacking endogenous gamma-tubulin. Immunofluorescence microscopy showed that these cells contained normal mitotic spindles and interphase microtubule arrays, and that human gamma-tubulin, like S. pombe gamma-tubulin, localized to spindle pole bodies, the fungal microtubule-organizing centers. These results demonstrate that human gamma-tubulin functions in fission yeast, and they suggest that in spite of the great morphological differences between the microtubule-organizing centers of humans and fission yeasts, gamma-tubulin is likely to perform the same tasks in both. They suggest, moreover, that the proteins that interact with gamma-tubulin, including, most obviously, microtubule-organizing center proteins, must also be conserved. We have also found that a fivefold overexpression of S. pombe gamma-tubulin causes no reduction in growth rates or alteration of microtubule organization. We hypothesize that the excess gamma-tubulin is maintained in the cytoplasm in a form incapable of nucleating microtubule assembly. Finally, we have found that expression of human gamma-tubulin or overexpression of S. pombe gamma-tubulin causes no significant alteration of resistance to the antimicrotubule agents benomyl, thiabendazole, and nocodazole.