Speaker: Adam D. Rudner Department of Cell Biology, Harvard Medical School, Boston, MA, USA Soon to arrive at OISB and BMI, Ottawa, ON, Canada The Phospho-proteome of the Anaphase Promoting Complex The exit from mitosis in eukaryotes is triggered by the regulated destruction of Securin and CyclinB by the Anaphase Promoting Complex (APC), a multi-subunit ubiquitin ligase. The APC also regulates other cell cycle transitions by targeting other proteins for degradation. In the budding yeast, Saccharomyces cerevisiae, the APC is composed of 13 subunits and its activity is regulated by the binding of activating subunits, the presentation of its substrates, and by its phosphorylation. The cyclin dependent kinase, Cdk1, phosphorylates the APC and this phosphorylation is required for its activation during mitosis. In an effort to determine if phosphorylation regulates other aspects of APC function we are determining the complete phospho-proteome of the APC using mass spectrometry. To date we have identified 62 phosphorylation sites on eight of the thirteen subunits. We are now using stable isotope labeling by amino acids in cell culture (SILAC) and absolute quantification (AQUA) to identify which sites are regulated during the cell cycle and in response to changes in cell physiology, as well to determine which kinases and phosphatases regulate APC phosphorylation.