Most proteins that regulate intracellular processes are constructed in a modular fashion from a combination of interaction and catalytic domains. Interaction domains mediate the formation of multi-protein complexes that confine signaling proteins to appropriate subcellular locations and help determine the specificity of enzyme-substrate interactions. In addition, extracellular protein domains mediate interactions between adjacent cells and help control higher order processes such as the formation of nerve synapses in the brain. To date, biologists and biochemists have typically studied protein-protein interactions one at a time. While reductionism has provided a detailed understanding of individual components, it has been less successful in uncovering the complex function of biological systems. The goal of my lab is to identify, characterize, and perturb large collections of proteins or protein domains as a first step in understanding how the cell exploits molecular recognition to regulate complex processes such as protein trafficking, intercellular communication, growth factor signaling, and apoptosis.