FIG. 2.

Visualization of virus particles by STEM. This dark-field electron micrograph shows a field with six RCASBP-AP particles. The three indicated by arrowheads were used for mass measurements as described in the text. (The other three could not be used because one is not fully visible, one is too close to a TMV, and one is too close to a contaminating mass.) The arrows point to TMV particles (used as an internal control). Some smaller contaminants can be seen in the background; it is possible that these are similar to microvesicles described by Ott et al. (20). The full scale of the micrograph is 1.024 μm.