You have been studying the synapse by electron microscopy and wish to learn more about proteins of the postsynaptic density (PSD). How would you begin to characterize PSD proteins? How would you pinpoint one protein (protein X) to characterize further? How would you obtain information about this protein and obtain its cDNA? What would you do with the cDNA to discover its binding proteins? How would you study protein X binding proteins in neuronal cells and their association with protein X?