Postsynaptic protein required for clustering of nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction. Expressed in muscles and neurons. Ubiquitinated by the BCR(kel-8) complex in the absence of unc-29, leading to its degradation. Mutants are resistant to levamisole, an agonist of nAChRs. Belongs to the RAPsyn family.