Complementation and phenotypic stabilization of vesicular stomatitis virus temperature-sensitive and thermolabile mutants by avian myeloblastosis virus

Cytoplasmic domain requirement for incorporation of a foreign envelope protein into vesicular stomatitis virus

Incorporation of human immunodeficiency virus type 1 (HIV-1) envelope proteins into vesicular stomatitis virus (VSV) particles was studied in a system that allows expressed envelope proteins to rescue phenotypically a temperature-sensitive mutant of VSV (tsO45). This mutant exhibits defective transport of its own envelope glycoprotein (G) and can be rescued by simultaneous expression of wild-type G protein from cDNA. We report here that a hybrid HIV-1-VSV protein containing the extracellular and transmembrane domains of the HIV-1 envelope protein fused to the cytoplasmic domain of VSV G protein was able to rescue the tsO45 mutant lacking the G protein, while the wild-type HIV-1 envelope protein was not. The VSV(HIV) pseudotypes obtained infected only CD4+ cells and were neutralized specifically by anti-HIV-1 sera. Our results indicate that the cytoplasmic tail of the VSV glycoprotein contains an independent signal capable of directing a foreign protein into VSV particles. The VSV(HIV) pseudotypes generated here were prepared in the absence of HIV-1 and should be useful for identifying molecules that block HIV-1 entry.

Heterogeneity of vesicular stomatitis virus particles: implications for virion assembly

Vesicular stomatitis virus (VSV) particles formed at early times after infection contain only one-third the amount of viral glycoportein (G protein), relative to the major internal structural proteins M and N, as is found in particles released later. These "early" particles also have a lower density in equilibrium sucrose gradients than do those formed later; however, the sedimentation velocity and specific infectivity of these two classes of particles are the same. VSV-infected cells also release virus-like particles which sediment considerably faster than authentic virions and contain a higher-than-normal proportion of the VSV G protein relative to internal VSV proteins. These particles have a reduced specific infectivity but a normal density in sucrose gradients. All classes of VSV virions contain a constant proportion of M and N polypeptides. The ratio of G protein to M or N protein, in contrast, can vary over a sixfold range; this implies that an interaction between a precise number of surface G proteins with either of the underlying M and N proteins is not a prerequisite for budding of infectious viral particles from the cell surface.

Mechanism of formation of pseudotypes between vesicular stomatitis virus and murine leukemia virus

Pseudotypes of vesicular stomatitis virus (VSV) and Moloney murine leukemia virus (MuLV), defined by their resistance to neutralization by anti-VSV antiserum, are released preferentially at early times after infection of MuLV-producing cells with VSV. At later times, after synthesis of MuLV proteins has been inhibited by the VSV infection, neither MuLV virions nor the VSV (MuLV) pseudotypes are made. Infection of MuLV-producing cells with mutants of VSV having temperature-sensitive lesions in either G or M protein does not generate pseudotypes at nonpermissive temperature, indicating that both proteins are needed for pseudotypes to form. Although the pseudotypes resist neutralization by anti-VSV serum, they are inactivated by anti-VSV serum plus complement, and they can be precipitated by rabbit anti-VSV serum plus goat anti-rabbit IgG. These results, coupled with experiments using a temperature-sensitive mutant of VSV G protein grown at partly restrictive temperature, suggest that small numbers of VSV G protein are obligately incorporated into VSV(MuLV) pseudotypes. There appears to be a stringent requirement for recognition of the viral core by homologous envelope components as the nucleating step in the budding process. Only after such a nucleation can the envelope components of the second virus substitute into the membrane of the budding particle.

Biological and electron microscopic studies on the phenotypic mixing of the thermolabile mutant of vesicular stomatitis virus, tl-17, with avian RNA tumor viruses

A thermolabile as well as thermosensitive mutant of vesicular stomatitis virus, VSV-tl-17, could be thermostabilized by phenotypic mixing with avian RNA tumor viruses (ATV). Biological, immunological and morphological studies revealed that this effect is due to a replacement of the thermolabile projections of the VSV by the avian tumor viral projections. The arrangement of projections of VSV and ATV on phenotypically mixed viria was studied by electron microscopy. A-type particles were detected in chick embryo cells which were doubly infected by ATV and VSV. Their intracytoplasmic appearance seemed to be the result of a disturbed maturation of ATV due to the relative deficiency of envelope proteins which were depleted by VSV maturation in the course of phenotypic mixing.

Phenotypic mixing of vesicular stomatitis virus and D-type oncornavirus

After mixed infection of cells with vesicular stomatitis virus (VSV, thermolabile mutant tl 17) and oncornavirus type D, phenotypically mixed virions are formed containing the VSV genome and oncornavirus and VSV envelope. The virions are thermostable and have serologic characteristics of both viruses.