Ligand-gated ion channels mediate the action of neurotransmitters at chemical synapses throughout the central nervous system. These receptors serve as the site of action of major classes of drugs such as barbiturates, tranquilizers, nicotine and muscle relaxants. One of them, the acetylcholine receptor (AChR)at the neuromuscular junction, is the target of attack for antibodies in the autoimmune disease, myasthenia gravis. All of the receptors in this family appear to be constructed according to a common plan in which five subunits surround a central aqueous pore. The subunits are highly homologous and have similar domain structures. Our experiments will investigate the mechanisms of assembly of one member of the family, the nicotinic AChR of mouse muscle. We will study the folding and degradation of individual subunits of the AChR, the pathway of assembly of the oligomer, the mechanisms by which specific subunits recognize each other, and how the cell monitors whether or not correct assembly has occurred. Our studies will be performed using non-muscle cells that transiently express the AChR, muscle cells and an in vitro system for translation of proteins. We will also try to obtain association of subunit fragments to generate a nicotinic binding site in vitro. Because of their structural similarity, all members of the family of ligandgated ion channels are likely to use common mechanisms of assembly. Our experiments should thus yield general insights into how neuro- transmitter receptors are assembled. They are relevant for understanding how the differentiated postsynaptic membrane is generated, and how it is repaired after damage, such as occurs in myasthenia gravis.