Mutant γ-tubulin (right) results in extra basal bodies.

Cells tightly regulate the replication of centrioles, which form the heart of centrosomes. But Shang et al. (page 1035) have found a way to decouple duplication of basal bodies, which are the unicellular equivalent of eukaryotic centrioles, from the cell cycle. It appears that γ-tubulin function is necessary to repress inappropriate replication of basal bodies.

γ-Tubulin is essential for basal body and centriole assembly and maintenance, but whether it regulated their formation was unclear.

Using systematic mutagenesis in Tetrahymena, Shang et al. identified two point mutations in the nucleotide binding domain of γ-tubulin that caused overproduction of basal bodies. Moreover, the excess structures arose in the center of the cells, as well as at the periphery where basal bodies normally reside. Thus, the mutants may allow de novo formation of basal bodies.

Significantly, only one of the two mutant residues contacts a bound nucleotide, based on comparison to the crystal structure. Therefore, the researchers hypothesize that nucleotide binding per se is not involved in repressing basal body formation, but rather think there is a distinct inhibitor that binds to γ-tubulin and prevents replication. What that inhibitor might be is not yet clear. However, the team speculates that whatever it is, it is likely to be active in other species because the nucleotide binding domain of γ-tubulin is very highly conserved.