FIG 7.

Negative-stain EM images of representative samples from the urea denaturation experiments. Under native conditions (i.e., pH 5.0), both the P73G and wild-type virions are uniform and monodispersed. Upon incubation in the swelling buffer, the wild-type virions expand; their cores are penetrated by stain but are still well dispersed. In contrast, the P73G particles are more heterogeneous in shape and form large aggregates. The bottom figures show the differences between the wild type and the P73G mutant under swelling conditions in the presence of 3 M urea. In the case of the P73G mutant, while the major virus band reappears in the agarose gel at 3 M urea, this sample contains only disrupted virions.