The fine structure and morphogenesis of the envelope and nucleocapsid of goat poxvirus and infectious bovine rhinotracheitis virus: A freeze‐fracture study

Abstract

AbstractWe studied the morphology and morphogenesis of viral envelopes and nucleocapsids of goat poxvirus (GPV) and infectious bovine rhinotracheitis virus (IBRV) by means of the freeze‐fracture technique. The GPV at an early development stage was fractured in its middle, and the envelope was shown to be a bilayer of particles. The mature GPV was fractured between two monolayers of the envelope. These facts suggest that there is little lipid and mainly protein particles in the envelope at the early‐development stage, then the lipid inserts into the envelope during viral development. We found that there were still many intramembranous protein particles in protoplasmic fracture face (PF) and extracellular fracture face (EF) of the envelope of mature GPV in the cytoplasm, and fewer particles in the envelope of released GPV. In the envelope of mature IBRV, however, there were many more intramembrane protein particles in the PF face than that in the EF face. Spike‐like structures could be seen at the outer edge of the IBRV envelope at times. Protein particles were regularly arranged in the plasmic membranes contacting IBRV. This phenomenon seems to be related to IBRV release. The naked cores, empty capsids, and nucleocapsids of IBRV were assembled in the nucleus of infected cells at the same time. The assembled nucleocapsids could be divided into five types according to their different fracturing positions, whose morphology was observed after deep etching. The morphology of the samples prepared with different methods was compared as well.