This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Centrosomes, the major microtubule organizing centers in animal cells, perform critical functions in cell organization, polarity and division. Abnormalities in centrosome number, size and morphology have been observed in nearly all human tumor types. Depletion of four proteins (SPD-2, SPD-5, PLK-1 and Aurora-A kinase (AIR- 1)) was shown to have severe defects in the recruitment of pericentriolar material (PCM). This recruitment defect results in centrosomes that are unable to nucleate the proper number of microtubules and ultimately experience catastrophic mitotic defects as proper mitotic spindles do not form. Our goal is try to understand the mechanistic relationship between SPD-2, SPD-5, PLK-1 and AIR-1 by assessing the importance of the kinase activity of AIR-1 and PLK-1 for centrosome assembly, and by using a combination of in vitro and in vivo approaches to determine if SPD- 2 and/or SPD-5 are activators or susbstrates of Aurora-A kinase. Through our collaboration with The Center for Physiological Proteomics (CPP), we will use mass spectrometry after in vitro kinase assays of SPD-5 and SPD-2 with both kinases AIR-1 and PLK-1 to identify the sites that are modified by phosphorylation. The contribution from CPP will therefore be crucial to understanding centrosome assembly and function will therefore impact on our understanding of cancer, metastasis and development.