The importance of the PCM to the fate of a cell and the organism itself is well documented 6. Additionally, formation of a daughter centriole occurs in the PCM, with the PCM appearing to have essential roles in this process 2, 5. The PCM must assemble around a centriole, as the PCM is necessary for the resulting centrosome to function by serving as the principal site for microtubule nucleation and anchoring 1, 2, 3, 4. The centrosome consists of a pair of centrioles surrounded by an amorphous protein network of pericentriolar material (PCM). In summary, PCM assembly begins in the cytosol where Sas-4 provides a scaffold for pre-assembled cytoplasmic complexes before tethering of the complexes in a centrosome. Finally, purified S-CAP complexes or recombinant Sas-4 can bind centrosomes stripped of PCM, whereas recombinant CNN or Asl cannot. When Sas-4 is mutated, so that it cannot form S-CAP complexes, centrosomes are present but with dramatically reduced levels of PCM. When Sas-4 is absent, nascent procentrioles are unstable and lack PCM, and functional centrosomes are not generated. In this study, we show that Sas-4 provides a scaffold for cytoplasmic complexes (named S-CAP), which include CNN, Asl and D-PLP, proteins that are all found in the centrosomes at the vicinity of the centriole. A centrosome consists of a pair of centrioles surrounded by a protein network of pericentriolar material (PCM) that is essential for the centrosome's function. Centrosomes are conserved organelles that are essential for accurate cell division and cilium formation.
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