FIG 4.

Upon poliovirus expansion, the topography of the outer surface changes dramatically. (A) A portion of the outer surface of the 135S reconstruction (right), viewed along a 2-fold axis, is compared with the corresponding density (left), calculated from the crystallographic model of mature poliovirus to 6 Å. Models of VP1, VP2, and VP3 are blue, yellow, and red, respectively, and symmetry axes are numbered. Shifts of the beta barrels cause a large hole to open at the 2-fold axis in 135S particles, as seen in a closeup comparison view. (B) The opening of a smaller hole at the quasi-3-fold (yellow asterisk) is associated with the shift or rearrangement nearby loops (as labeled). In the 135S reconstruction, in the upper right of the panel, the disordering of density for the VP2 propeller tip is dramatic.