2 TYPES OF VIRUS-RELATED PARTICLES ARE FOUND DURING TRANSMISSIBLE GASTROENTERITIS VIRUS MORPHOGENESIS

The intracellular assembly of the transmissible gastroenteritis corona virus (TGEV) was studied in infected swine testis (ST) cells at differ ent postinfection times by using ultrathin sections of conventionally embedded infected cells, freeze substitution, and methods for detectin g viral proteins and RNA at the electron microscopy level. This ultras tructural analysis was focused on the identification of the different viral components that assemble in infected cells, in particular the sp herical, potentially icosahedral internal core, a new structural eleme nt of the extracellular infectious coronavirus recently characterized by our group. Typical budding profiles and two types of virion-related particles were detected in TGEV-infected cells. While large virions w ith an electron-dense internal periphery and a clear central area are abundant at perinuclear regions, smaller viral particles, with the cha racteristic morphology of extracellular virions (exhibiting compact in ternal cores with polygonal contours) accumulate inside secretory vesi cles that reach the plasma membrane. The two types of virions coexist in the Golgi complex of infected ST cells. In nocodazole-treated infec ted cells, the two types of virions coexist in altered Golgi stacks, w hile the large secretory vesicles filled with virions found in normal infections are not detected in this case. Treatment of infected cells with the Golgi complex-disrupting agent brefeldin A induced the accumu lation of large virions in the cisternae that form by fusion of differ ent membranous compartments. These data, together with the distributio n of both types of virions in different cellular compartments, strongl y suggest that the large virions are the precursors of the small viral particles and that their transport through a functional Golgi complex is necessary for viral maturation.