ASSEMBLY OF VACCINIA VIRUS - THE 2ND WRAPPING CISTERNA IS DERIVED FROM THE TRANS-GOLGI NETWORK

During the assembly of vaccinia virus, the intracellular mature virus becomes enwrapped by a cellular cisterna to form the intracellular env eloped virus (IEV), the precursor of the extracellular enveloped virus (EEV). In this study, we have characterized the origin of this wrappi ng cisterna by electron microscopic immunocytochemistry using lectins, antibodies against endocytic organelles, and recombinant vaccinia vir uses expressing proteins which behave as Golgi resident proteins. No l abelling for endocytic marker proteins could be detected on the wrappi ng membrane. However, the wrapping membrane labelled significantly for a trans Golgi network (TGN) marker protein. The recycling pathway fro m endosomes to the TGN appears to be greatly increased following vacci nia virus infection, since significant amounts of endocytic fluid-phas e tracers were found in the lumen of the TGN, Golgi complex, and the w rapping cisternae. Using immunoelectron microscopy, we localized the v accinia virus membrane proteins VV-p37, VV-p42, VV-p21, and VV-hemaggl utinin (VV-HA) in large amounts in the capping cisternae, in the outer membranes of the IEV, and in the outermost membrane of the EEV. The b ulk of the cellular VV-p37, VV-p21, and VV-p42 were in the TGN, wherea s VV-HA was also found in large amounts on the plasmamembrane and in e ndosomes. Collectively, these data argue that the TGN becomes enriched in vaccinia virus membrane proteins that facilitate the wrapping even t responsible for the formation of the IEV.