A putative ariadne-like E3 ubiquitin ligase (PAUL) that interacts with the muscle-specific kinase (MuSK)

Formation of the postsynaptic membrane at the skeletal neuromuscular junction (NMJ) requires activation of the muscle-specific receptor tyrosine kinase (MuSK). Few intracellular mediators or modulators of MuSK actions are known. E3 ubiquitin ligases may serve this role, because activities of several receptor tyrosine kinases, G-protein-coupled receptors and channels are modulated by ubiquitination. Here, we report identification of a putative Ariadne-like ubiquitin ligase (PAUL) that binds to the cytoplasmic domain of MuSK. PAUL is expressed in numerous tissues of developing and adult mice, and is present at NMJs in muscle fibers but is not confined to them.