Impact of Vesicular Stomatitis Virus M Proteins on Different Cellular Functions (original) (raw)
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Journal of Virology, 2002
The matrix (M) protein of vesicular stomatitis virus (VSV) is a multifunctional protein that is responsible for condensation of the ribonucleocapsid core during virus assembly and also plays a critical role in virus budding. The M protein is also responsible for most of the cytopathic effects (CPE) observed in infected cells. VSV CPE include inhibition of host gene expression, disablement of nucleocytoplasmic transport, and disruption of the host cytoskeleton, which results in rounding of infected cells. In this report, we show that the VSV M gene codes for two additional polypeptides, which we have named M2 and M3. These proteins are synthesized from downstream methionines in the same open reading frame as the M protein (which we refer to here as M1) and lack the first 32 (M2) or 50 (M3) amino acids of M1. Infection of cells with a recombinant virus that does not express M2 and M3 (M33,51A) resulted in a delay in cell rounding, but virus yield was not affected. Transient expression...
Separate pathways of maturation of the major structural proteins of vesicular stomatitis virus
Journal of virology, 1977
Cell fractionation and protein electrophoresis were used to study the intracellular sites of synthesis and intermediate structures in the assembly of the virion proteins of vesicular stomatitis virus. Each of the three major virion proteins assembled into virions through a separable pathway. The nucleocapsid (N) protein was first a soluble protein and later incorporated into free, cytoplasmic nucleocapsids. A small amount of N protein was bound to membranes at later times, presumably representing either nucleocapsids in the process of budding or completed virions attached to the cell surface. The matrix (M) protein also appeared to be synthesized as a soluble protein, but was then directly incorporated into membranous structures with the same density as whole virus. Very little M protein was ever found in membranes banding at the density of plasma membranes. The M protein entered extracellular virus very quickly, as though it moved directly from a soluble state into budding virus. I...
Journal of virology, 1995
Transfection of mammalian CV1 cells with a recombinant M-gene pTM1 plasmid, driven by vaccinia virus-expressed phage T7 polymerase, resulted in the expression of matrix (M) protein, which is progressively released from the exterior surface of the transfected-cell plasma membrane. Exocytosis of M protein begins 2 to 4 h posttransfection and reaches a peak by 10 to 16 h posttransfection; dye uptake studies reveal that > 97% of cells are alive and have intact membranes at 16 h posttransfection. Density gradient centrifugation and labeling with radioactive palmitic acid revealed that the M protein is released from cells in association with lipid vesicles. Expression of M-gene deletion mutants suggests that exocytosis of M protein requires the presence of a membrane-binding site at N-terminal amino acids 1 to 50. Cells transfected with the pTM1 plasmid containing the M gene of the temperature-sensitive mutant tsO23 expressed ample quantities of the mutant M protein at permissive (31 d...
The recent solution of the crystal structure of a fragment of the vesicular stomatitis virus matrix (M) protein suggested that amino acids 121 to 124, located on a solvent-exposed loop of the protein, are important for M protein self-association and association with membranes. These residues were mutated from the hydrophobic AVLA sequence to the polar sequence DKQQ. Expression and purification of this mutant from bacteria showed that it was structurally stable and that the mutant M protein had self-association kinetics similar to those of the wild-type M protein. Analysis of the membrane association of M protein in the context of infection with isogenic recombinant viruses showed that both wild-type and mutant M proteins associated with membranes to the same extent. Virus expressing the mutant M protein did show an approximately threefold-lower binding affinity of M protein for nucleocapsid-M complexes. In contrast to the relatively minor effects of the M protein mutation on virus assembly, the mutant virus exhibited growth restriction in MDBK but not BHK cells, a slower induction of apoptosis, and lower viral-protein synthesis. Despite translating less viral protein, the mutant virus produced more viral mRNA, showing that the mutant virus could not effectively promote viral translation. These results demonstrate that the 121-to-124 region of the VSV M protein plays a minor role in virus assembly but is involved in virus-host interactions and VSV replication by augmenting viral-mRNA translation.
Virology, 1997
In addition to its function in virus assembly, the viral matrix (M) protein of vesicular stomatitis virus (VSV) inhibits hostdirected gene expression. The goal of this study was to determine whether sequence changes in M protein contribute to a reduced shut off of host gene expression in cells persistently infected with VSV. Viruses isolated from L cells persistently infected with VSV inhibited host RNA synthesis more slowly than wild-type (wt) VSV. M genes of the persistent viral population were cloned and sequenced. One mutation, an N to D change at position 163 of the protein sequence (N163D), was common to all the molecular clones. The N163D M protein was synthesized from transfected mRNA at a rate that was 30% of that of wt M protein, but was turned over at a rate that was similar to that of wt M protein. Transfection of mRNA encoding N163D M protein inhibited expression of a cotransfected target gene encoding chloramphenicol acetyl transferase (CAT), but the inhibition was 6 to 10 times less effective than transfection of equivalent amounts of wt M mRNA. This difference could not be accounted for by differences in translation of CAT mRNA. Thus, when the differences in M protein expression were taken into account, N163D M protein was 2 to 3 times less effective than wt M protein in the inhibition of host-directed gene expression, similar to the differences in host transcription observed in virus-infected cells. Point mutations in addition to the N163D mutation were found in about half of the M gene molecular clones. The M gene of an independently isolated molecular clone, N163D.2, contained two additional point mutations in its carboxy terminal region. N163D.2 M protein was highly defective in inhibition of host gene expression and was turned over more rapidly than wt M protein. These results support the idea that M gene mutations contribute to a reduced cytopathic effect in cells persistently infected with VSV.
Journal of Virology, 1977
We report here an in vitro system designed to study the interactions of vesicular stomatitis virus (VSV) proteins with cellular membranes. We have synthesized the VSV nucleocapsid (N) protein, nonstructural (NS) protein, glycoprotein (G protein), and membrane (M) protein in a wheat germ, cell-free, protein-synthesizing system directed by VSV 12 to 18S RNA. When incubated at low salt concentrations with purified cytoplasmic membranes derived from Chinese hamster ovary cells, the VSV M and G proteins bind to membranes, whereas the VSV N and NS proteins do not. The VSV M protein binds to membranes in low or high divalent cation concentrations, whereas binding of significant amounts of G protein requires at least 5 mM magnesium acetate concentrations. Vesicular stomatitis virus (VSV) is a simple, lar membranes, whereas the VSV N and NS enveloped virus that contains two membrane proteins do not. proteins: the glycoprotein (G protein), which forms the spikes of the virion (4, 23), and the MATERIALS AND METHODS membrane (M) protein, which lines the inner Cells and viruses. Membranes were prepared surface of the viral membrane (3). There are from CHO cells. Stocks of VSV (pure B particles of three other known viral proteins, the VSV nuthe Indiana serotype) were grown in CHO cells and cleocapsid (N) protein, the nonstructural (NS) purified as described previously (20). protein, and the viral transcriptase (L) protein. Preparation of VSV 12-186 polyribosomal RNA. These three proteins are associated with the The procedure described by Palmiter (15) was used core ofthe virus particle (16, 23, 24). Each of the with several modifications for the preparation of five viral proteins is synthesized from a mono-VSV 12-18S polyribosomal RNA. CHO cells growing cistronic mRNA (9, 13, 14). at 37°C were infected with VSV at a multiplicity of 3 risngtic m arNAl(9 13, 14). PFU/cell as described previously (20), except that 5 During the early stages in the maturation Of~.tg of actinomycin D per ml was added at the beginthis virus, host cell membranes are modified ning of infection. [3H]uridine (70 Ci/mmol, 25 ,uCi/ with the VSV G and M proteins. Cell fractionaml; New England Nuclear Corp.) was added 2 h tion studies of VSV-infected cells have shown postinfection. Infected cells were harvested at 4.5 h that the VSV M and G proteins rapidly become postinfection, suspended in sucrose-TKM buffer associated with the membrane fraction of the (0.05 M Tris [pH 7.5], 0.025 M KCl, 0.005 M magnecells after their synthesis (5, 11, 12, 24). Nucleo-sium acetate, 0.25 M sucrose), and disrupted with 10 capsid structures containing the genome RNA strokes of a tight-fitting Dounce homogenizer. Nuas well as the viral N, NS, and L proteins are clei were removed by centrifugation (1,000 x g for 2 asswemlld as the vira plaNsm. andsLptroteisures min). The resulting cytoplasmic extract was centriassembled in the cytoplasm. These structures fuged at 20,000 x g for 20 min, and the pellet (mem