Fig. 2.

Receptors are bound to up to three rapsyn lobes. (A–E) Averages obtained after classification as viewed parallel to the membrane (top of each pair) or from the cytoplasm (bottom of each pair). The position of the plasma membrane is represented by two dashed lines in A, and the location of a masked out neighboring receptor is indicated by a dashed outline in B. A variable number of rapsyn lobes is observed in the different class averages. When more than one lobe is present, the different lobes are labeled with roman numerals. The ratio r between the volume of each lobe and the theoretical volume of one rapsyn molecule is shown. Represented at the lower right of the figure are the surface contours of class averages C, D, and E, in a 1-voxel-thick slice located at the level of the rapsyn lobes. Position I is occupied in class averages C and E; position II in class average C, D, and E; and position III in class average D and E. The relative numbers of receptors sorted to the different classes are (from class A to E) 21.5%, 23.1%, 16.5%, 20.1%, and 18.8%.