Effect of impaired glycosylation on the synthesis of envelope proteins of Rauscher murine leukemia virus

Cytochalasin B inhibits the maturation of measles virus

The release of measles virus was studied in the presence of cytochalasin B (CB), a drug that disrupts actin microfilaments. In the presence of CB, infected cells accumulated infectious virus while virus released from these cultures decreased drastically (up to 99% inhibition). Electron micrographs showed that viral buds were reduced and had an unusual distribution along the cell membrane in CB-treated cultures. CB inhibition of released virus occurred rapidly (within 30 min) and to a full extent even when the drug was added during the final 2 hr of a 48-hr replicative cycle. CB inhibition of cellular functions is reversible and, similarly, inhibition of virus release could be almost completely reversed within 30 min after the drug was removed. Since CB can also inhibit sugar transport and protein glycosylation, 2-deoxy-D-glucose (DG) was used to study the manifestations of glycosylation inhibition. DG inhibited virus production only when added during the first one-third of the replicative cycle and inhibited cell-associated and released virus to an equal extent. Cytochalasin D, which disrupts microfilaments without affecting protein glycosylation, caused an inhibition of virus release analogous to the inhibition caused by CB. Thus, alteration of microfilament structure alters the normal budding process of measles virions. This suggests that microfilaments may play a role in the release of budding virions.

Cellular response to rabies virus infection

The effects of rabies virus on host cells were studied and compared to those obtained with another rhabdovirus, vesicular stomatitis virus [J. Virol. 34, 777-781 (1980)]. We show here: (1) that rabies infection has no effect on cell morphology, while infection with vesicular stomatitis virus caused cell retraction. Thus, only vesicular stomatitis virus induced a depolymerization of the microfilaments; and (2) that microtubules and microfilaments do not play a major role in rabies virus production, as it is suggested by results obtained with several effectors (colcemid, colchicine and cytochalasin-B) which directly or indirectly affect cytoskeleton organization. The same properties were observed with directly or indirectly affect cytoskeleton organization. The same properties were observed with vesicular stomatitis virus. Furthermore, the use of cytochalasin-B shows that an inhibition of glycosylation of the virion spike protein occurs only in rabies infected cells. As vesicular stomatitis viral glycosylation is normal in cytochalasin-B treated cells, results obtained indicate that two types of interactions can occur between a virion and the host-cell depending on the rhabdovirus type.

Surface expression of murine leukemia virus structural polypeptides on host cells and the virion

The expression of murine leukemia virus structural polypeptides on the surface of cells producing exogenous Friend leukemia virus, endogenous ecotropic AKR and xenotropic BALB/c virus was investigated. Antisera to Friend virus gp71, p30, p15E, p12 and p10 were employed in a complement-dependent chromium release assay and to immunoprecipitate lactoperoxidase iodinated surface polypeptides prior to analysis in polyacrylamide gel electrophoresis. With the latter technique gag-gene encoded proteins and their precursors were not discovered on the viral and cellular surface membranes. Only env-gene encoded polypeptides gp85, gp71, and p15E were detectable. p15E is embedded into the lipid membrane. gp85 is formed by disulfide linkage of p15E to surface-exposed gp71. The ratio of gp71 to gp85 is variable and apparently determined by the host cell. Antibodies of strong cytotoxicity are those against type- and group-specific epitopes of gp71 as well as type-specific epitopes of p12.

Analysis of a 5' leader sequence on murine leukemia virus 21S RNA: heteroduplex mapping with long reverse transcriptase products

The majority of the mRNA that specifies retrovirus glycoproteins is known to be derived from the 3' half of the genome. To examine whether the glycoprotein mRNA of murine leukemia viruses (MuLVs) might consist of portions derived from both the 5' and 3' ends of the viral genome, we performed hybridization with a 5'-specific probe and heteroduplex analysis with long reverse transcribed DNA. A 5' probe was made by purifying a discrete 50 nucleotide-long reverse transcript attached to its tRNA primer. This probe was found to hybridize to RNA of the size of glycoprotein mRNA--21S, poly(A)-containing RNA--indicating that the mRNA could have a 5' leader sequence. The 5'-specific sequences were studied by electron microscopic examination of hybrids between 21S RNA and the two longest discrete cDNA species synthesized in the endogenous reverse transcriptase reaction. One of these species, 8.8 kb long, is only made in the absence of actinomycin D, but it does not contain any self-complementary sequences, and therefore appears to be a complete transcript of the viral genome. The shorter of the two species, 8.2 kb long, is synthesized whether or not actinomycin D is present; it must terminate 500--600 nucleotides internal to the 5' end of the template RNA. The structures observed in heteroduplexes of 21S RNA and these DNAs indicated the presence of a leader sequence approximately 500 nucleotides long at the 5' end of the 21S RNA. Sequences comprising this leader segment in the 21S RNA mapped at the 5' end of the genome RNA; the rest of the 21S RNA consisted of sequences from the 3' portion of the genome. Analysis of heteroduplexes with 8.2 kb DNA suggested that actinomycin D could block the reverse transcription of most of the sequence in the genome RNA that appears as a leader in the 21S RNA.