Project Summary/Abstract The nucleosome is the hub of signals that regulate gene expression in eukaryotic cells. An important mechanism of such regulation is the post-translational modification of the histone protein components of the nucleosome. However, we possess only a rudimentary mechanistic understanding for how these modifications are installed on the physiological nucleosome substrates by histone modification enzymes and subsequently read by epigenetic reader proteins. These shortcomings limit our ability to interpret the wealth of genetic, genomic and biochemical data available, and they hamper development of new therapeutics that target epigenetic chromatin enzymes and readers associated with human diseases including cancer. We are focused on addressing these deficiencies through structural and biochemical studies of histone modification enzymes and readers in complex with the nucleosome. We leverage structural models produced using cryoelectron microscopy to develop mechanistic hypotheses and then challenge these models through nucleosome-based binding and enzymatic assays. Our studies of epigenetic histone modification enzymes and readers should impact both our basic science understanding of gene regulation and therapeutics for human diseases.