Tubulin nucleotide status controls Sas-4-dependent pericentriolar material recruitment

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Abstract
Avidor-Reiss and colleagues show that the nucleotide status of tubulin regulates recruitment of pericentriolar material. Binding of GTP-bound tubulin to the Sas-4 centrosomal protein prevents the Sas-4-dependent formation of centrosomal protein complexes, whereas the Sas-4-stimulated hydrolysis of tubulin–GTP into tubulin–GDP has the opposite effect. Regulated centrosome biogenesis is required for accurate cell division and for maintaining genome integrity1. Centrosomes consist of a centriole pair surrounded by a protein network known as pericentriolar material1 (PCM). PCM assembly is a tightly regulated, critical step that determines the size and capability of centrosomes2,3,4. Here, we report a role for tubulin in regulating PCM recruitment through the conserved centrosomal protein Sas-4. Tubulin directly binds to Sas-4; together they are components of cytoplasmic complexes of centrosomal proteins5,6. A Sas-4 mutant, which cannot bind tubulin, enhances centrosomal protein complex formation and has abnormally large centrosomes with excessive activity. These results suggest that tubulin negatively regulates PCM recruitment. Whereas tubulin–GTP prevents Sas-4 from forming protein complexes, tubulin–GDP promotes it. Thus, the regulation of PCM recruitment by tubulin depends on its GTP/GDP-bound state. These results identify a role for tubulin in regulating PCM recruitment independent of its well-known role as a building block of microtubules7. On the basis of its guanine-bound state, tubulin can act as a molecular switch in PCM recruitment.

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