Electron microscopy study of reovirus reaction cores.

A combined staining and shadowing method has been used to enhance the contrast of both reovirus cores and the RNA product that they have synthesized. After limited synthesis when all RNA strands associated with the core are nascent, many cores are observed that have more than 10 strands associated with each particle. The lengths of individual nascent mRNA molecules are not identical: many strands are extruded in the form of loops. These observations are consistent with the notion that synthesis of individual mRNA molecules occurs simultaneously at different rates at a number of different sites. The sites of extrusion are probably the 12 hollow projections located on the surface of the core.