Fig. 4. FIGQY-phosphorylation occurs at the vertebrate neuromuscular junction. ACh receptors at the rat neuromuscular junction as labeled by bungarotoxin (A,D) are confined to the crests of junctional folds while ankyrin G (B) is confined to the deep regions of these folds in muscle cell plasma membrane. The two distributions do not overlap (C, arrows indicate identical position in all three images). FIGQY-phosphorylation (E) is strictly confined to the crests of junctional folds with ACh receptors (D) but has a more punctate distribution than ACh receptors. Composite images are shown in C,F. Scale bar: 2 µm. N, location of nerve terminals; M, muscle cell.