The existence of γ-tubulin was first reported approximately ten years ago, and it is appropriate to review the progress that has been made in γ-tubulin research and to discuss some of the unanswered questions about γ-tubulin function. γ-Tubulin is ubiquitous in eukaryotes and is generally quite conserved. Two highly divergent γ-tubulins have been discovered, however, one in Saccharomyces cerevisiae and one in Caenorhabditis elegans. Several organisms have two γ-tubulin genes. In Drosophila melanogaster, the two γ-tubulins differ significantly in sequence and expression pattern. In other organisms the two γ-tubulins are almost identical and expression patterns have not been determined. γ-Tubulin is located at microtubule organizing centers in many organisms, and it is also frequently associated with the mitotic spindle. γ-Tubulin is essential for the formation of functional mitotic spindles in all organisms that have been examined to date. In animal cells, complexes containing γ-tubulin are located at microtubule organizing centers where they nucleate the assembly of microtubles. In spite of the considerable progress that has been made in γ-tubulin research important questions remain to be answered. The exact mechanisms of microtubule nucleation by γ-tubulin complexes remain to be resolved as do the mechanisms by which microtubule nucleation from γ-tubulin complexes is regulated. Finally, there is evidence that γ-tubulin has important functions in addition to microtubule nucleation, and these functions are just beginning to be investigated.
1999 by Japan Society for Cell Biology