FIG. 2.

(A) The radial density profile of the membrane region of mature MMTV. Radial density profiles for eight MMTV virions were aligned and averaged. The two largest peaks correspond to the inner (left) and outer (right) leaflets of the bilayer. Outside the membrane, the glycoprotein consists of two distinct densities. The inset shows the schematic glycoprotein structure (black) with the lipid bilayer (grey), indicating the distances in nanometers between features. (B) A top view of the viral spike obtained by aligning, averaging, and applying threefold symmetry to images of 542 negatively stained spikes. Scale bar, 5 nm.