Morphological studies of Gross virus-induced lymphoblasts by scanning electron microscopy.

The surface of Gross virus-induced murine lymphoblasts and C-type virus particles budding from these cells were investigated under the scanning electron microscope (SEM). The cells appeared spindle-shaped or roughly-rounded with extensive surface features consisting of microvilli, blebs and ruffled membranes. C-type virus particles were detected on the cell membrane as small spherical particles, distinguishable from the microvilli. Clustered virions were observed in some cases. However, the distribution of virions appeared to be random. The surface of the virion was smooth and had no globular units at high magnification. These morphological observations were confirmed in ultrathin sections.

Morphological, chemical, and antigenic organization of mammalian C-type viruses.

New features in the architecture of mammalian type C viruses, in particular knoblike surface projections and hexagonally arranged subunits on the core shell could be demonstrated by electron microscopy, taking advantage of newly developed preparation techniques. As examples, murine leukemia viruses (MuLVs) and newly isolated porcine and bovine C viruses are presented. The major proteins of a MuLV were isolated and partially characterized in chemical terms and with respect to their serological and other biological activities, such as interfering and hemagglutinating (HA) capacity. Most of the characterized proteins could be localized in particular substructures of the virion either by selective removal or isolation of electron microscopically identifiable constituents. The information obtained allowed the design of a more detailed model of mammalian C viruses. Special attention was devoted to the further characterization of interspecies antigens of mammalian C viruses. Different antigenic determinants were revealed. Their distribution allows further subgrouping of mammalian C viruses.

Structural studies of retroviruses: characterization of oligomeric complexes of murine and feline leukemia virus envelope and core components formed upon cross-linking.

To examine the protein proximity and subunit organization of type C retroviruses, preparations of AKR murine leukemia virus were treated with bifunctional cross-linking reagents and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The cross-linked components obtained were characterized by immunoprecipitation with monospecific antisera against purified viral proteins, followed by SDS-PAGE analysis both before and after cleavage of the cross-links. With these procedures, complexes of both viral envelope and core components were identified. The major envelope subunit obtained was a large (apparent molecular weight of 450,000 to 500,000), glycosylated complex, composed of four to six gp70-p15(E) subunits. This complex was detected over a 100-fold range of cross-linker concentration and thus seems to represent a particularly stable viral substructure. The cross-linked complexes of the core proteins consisted of oligomers of p30 dimers, suggesting that the p30 dimer is a basic structural unit of the viral core. When virion preparations, which had previously been disrupted with the nonionic detergent Nonidet P-40, were cross-linked, the envelope complex was still observed, indicating that this structure is stable in the presence of Nonidet P-40. A similar envelope structure was observed for feline leukemia virus, suggesting that such a complex may be a conserved feature of oncornavirus structure.