 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 material ( pcm)1 . 
 pcm assembly is a tightly regulated , critical step that determines a centrosome s size and capability24 . here 
 , we report a role for tubulin in regulating pcm recruitment via 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 can not bind tubulin , enhances centrosomal protein complex formation and has abnormally large centrosomes with excessive activity . 
 these suggest that tubulin negatively regulates pcm recruitment . 
 whereas tubulin - gtp prevents sas-4 from forming protein complexes , tubulin - gdp promotes it . 
 thus , tubulin s regulation of pcm recruitment 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 . based on its guanine bound state , tubulin can act as a molecular switch in pcm recruitment . 
Supplementary Material