Speaker: Leslie Mitchell Currently working on a Ph.D. in the lab of Dr. Kristin Baetz at the University of Ottawa The Systematic Analysis of the NuA4 Histone Acetyltransferase In yeast, the NuA4 enzyme complex impacts genome stability through its known roles in DNA repair, transcription, and faithful chromosome segregation. NuA4 is a histone acetyltransferase, highly conserved in the orthologous human complex Tip60, that catalyzes the acetylation of histone H4, histone H2A, and the histone variant Htz1. However, the molecular mechanisms by which NuA4 mediates its known cellular processes are poorly understood. Furthermore, it is unclear whether NuA4 participates in additional cellular processes. NuA4 is composed of thirteen subunits, six of which are required for yeast cell viability including the catalytic subunit Esa1p, while the remaining seven subunits are non-essential. Because non-essential deletion mutants are particularly amenable to both biochemical and genetic analysis, systematic proteomic and genomic methods were utilized to map the physical and genetic interactions of the seven non-essential NuA4 subunits. Using a series of affinity purifications of the NuA4 complex, we defined the contribution of each non-essential NuA4 subunit to NuA4 complex integrity. Furthermore, using synthetic genetic array technology, genetic interactions were uncovered for all seven of the non-essential NuA4 subunits. Through these analyses, we have discovered an essential scaffolding role for the Eaf1p subunit in maintaining NuA4 complex integrity, and have shown the 150 genetic interactions of EAF1 are largely shared with a point mutant of the essential catalytic subunit, ESA1. In contrast to Eaf1p, deletion of each of the other non-essential subunits has minimal effect on NuA4 complex integrity. The genetic interactions displayed by these other subunits overlap with subsets of the EAF1/ESA1 genetic interaction profile, thereby suggesting the pathways through which these subunits contribute to NuA4 cellular roles. Integration of these data sets provides key insights into the both roles of the individual non-essential subunits within the NuA4 complex, as well as the NuA4 enzyme complex as a whole.