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Results for “Virus Assembly”

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At least 19 recordsLinked to original sources
PubMed1979

Kinetics and mechanism of tobacco mosaic virus assembly: direct measurement of relative rates of incorporation of 4S and 20S protein.

The mechanism of assembly of tobacco mosaic virus has been investigated under conditions in which the rates of incorporation of the 4S and 20S proteins can each be directly measured by analytical centfrifugation. Under these conditions, pH 6.5, 6.5 degrees C, 0.10 M ionic strength potassium orthophosphate, the protein can be made to exist as a metastable 20S aggregate that is necessary for efficient reconstitution. The overall assembly process consists of an initiation (nucleation) reaction that requires two to three 20S disk aggregates per RNA molecule and is followed by an elongation (growth) reaction. In the elongation phase of assembly the 4S protein is incorporated 50 to 70 times faster than the 20S disk, calculated on the basis of a steady-state kinetic analysis. Therefore, under these conditions, in which the rate of assembly is about 0.06 of that at pH 7, 20 degrees C, 0.10 M ionic strength orthophosphate, the 4S protein preferentially participates in the elongation phase. At this slow reconstitution rate intermediate assembly states (about 70-168 S) can be observed. The kinetics of both protein incorporation and nucleoprotein formation suggest that the elongation process is composed of at least two different, possibly sequential, rate-limiting reactions.

Kinetics↗
PubMed1978

Role of the host in virus assembly: cloning of the Escherichia coli groE gene and identification of its protein product.

Correct assembly of the heads of bacteriophages lambda and T4 requires the function of the groE gene of the Escherichia coli host. We have isolated a transducing derivative of lambda, called lambda gt-Ec.groE, that carries a functional copy of the groE gene. Unlike wild-type lambda, this phage is able to form plaques on hosts with a mutant groE gene. We have isolated an amber mutation in the groE gene carried by the phage, and this has made it possible to identify the groE product as a protein of molecular weight 65,000. In the phage, the groE gene is under the control of an early phage promoter.

Bacterial Proteins↗
PubMed1977

Antiviral protection by virus-immune cytotoxic T cells: infected target cells are lysed before infectious virus progeny is assembled.

Virus-immune cytotoxic T cells can inhibit effectively growth of vaccinia virus in acutely infected target cells in vitro by destroying infected target cells before infectious virus progeny is assembled. Together with the fact that virus-specific T cells are demonstrable after 3 days, very early during infection, and with strong circumstantial evidence from adoptive transfer models in vivo, these data suggest that in some virus infections T cells may in fact act cytolytically in vivo to prevent virus growth and spread and be an important early antiviral effector mechanism.

Animals↗
PubMed1977

Inside-out model for self-assembly of tobacco mosaic virus.

Incompletely reconstituted particles of tobacco mosaic virus treated with moderate concentrations of dimethylsulfoxide prior to electron microscopy have two visible tails of unencapsidated RNA, a long one and a short one. The short tail has a constant length of 720 +/- 80 nucleotides in incomplete particles of diverse size and probably corresponds to the 3'OH end of the RNA. The length of the long 5' tail is inversely related to the length of the unfinished rod. Surprisingly, both tails appear to protrude from the same end of the particle. These observations suggest that the strand of RNA coming out of one end of the particle loops back along the length of the rod so as to appear at the opposite end. The "looped-back" tail almost certainly passes down the empty central channel of the incomplete rod. The findings are compatible with a model of tobacco mosaic virus assembly in which the RNA inserts itself beneath layers of incoming protein from within the central channel.

Binding Sites↗
PubMed1976

Assembly of tobacco mosaic virus.

The assembly of tobacco mosaic virus requires the presence of a particular protein aggregate, the disk. During the nucleation, a specific region of the RNA interacts with a single disk, to bring about a necessarily cooperative transition from the paired two-layer structure to a short segment of nucleo-protein helix. There is a high selectivity for this region of the TMV RNA, because of the many nucleotides bound at once, and other nucleotide sequences appear only to bind by a different mechanism. Elongation of the nucleated rods can continue with either further disks or the less aggregated 'A-protein' as the protein source, but the continued cooperativity inherent with disks would have some advantages. The rates of the two processes have been separately determined and growth is faster when disks are still present. New experiments show that the breakdown of disks to yield A-protein is relatively slow and it is concluded that virus growth from disks could not proceed through a prior breakdown in solution, but must involve the direct interaction of the disk with the growing nucleoprotein rod. The detailed mechanism of disk addition is not understood but it may involve a directed breakdown, since there is also evidence for the existence of a non-equilibrium form of A-protein which has aggregation kinetics distinct from those of equilibrium A-protein. Some implications for the general assembly pathways of viruses both of the specificity and of the assembly/disassembly cycle during the viral infection are considered.

Kinetics↗
PubMed1979

Intracellular forms of simian virus 40 nucleoprotein complexes. II. Biochemical and electron microscopic analysis of simian virus 40 virion assembly.

The simian virus 40 virion assembly process was studied with pulse-labeling kinetics of virion proteins, CsCl gradient analysis, electron microscopy, and low-salt gel electrophoresis. The results obtained are consistent with the model of gradual addition and organization of capsid proteins around simian virus 40 chromatin. Empty virions, as observed in the CsCl gradient by previous workers, were found to be the dissociation product of immature virus. Histone H1 was found in simian virus 40 chromatin and virion assembly intermediates but not in the mature virion banding at 1.34 g/ml in the CsCl gradient.

Capsid↗
PubMed1975

Effect of lipid alkyl chain perturbations on the assembly of bacteriophage PM2.

The lipid-containing bacteriophage PM2 can produce infectious virus in cultures infected at temperatures up to 31.5 degrees C, but not at 34 degrees C. Its host, Pseudomonas BAL-31, grows at 34 degrees C and cultures infected at that temperature undergo lysis. Sucrose-gradient analysis shows that 34 degrees C lysates contain no PM2-like particles. Temperature-shift experiments establish that the thermally sensitive process is late in infection when virus assembly is taking place. Adamantanone, a small hydrophobic molecule that perturbs membrane hydrocarbon zones, prevents the production of infective virus. Concentrations which prevent virus production have no effect on host-cell growth or stability of mature virions. Adamantanone exerts its effects late in the infectious cycle, and lysates amde in its presence contain no PM2-like particles. These experiments, carried out at 25 degrees C, indicate that adamantanone prevents the assembly of stable PM2 virus. Spin-label studies suggest that the lipid alkyl chains of the host-cell membrane are in an "ordered" state at temperatures below about 33 degrees C and undergo a transition to a "disordered" state above that temperature. Furthermore, the addition of adamantanone perturbs the hydrocarbon zones, producing a greater degree of disorder even below 25 degrees C. Our findings suggest that the cell membrane can function and grow with the lipid alkyl chains in either the "ordered" or "disordered" state, but that the "ordered" state must be maintanined for PM2 assembly to occur.

Anti-Bacterial Agents↗
PubMed2025

Computational Insights on the Assembly of the Dengue Virus Membrane-Capsid-RNA Complex.

Dengue virus, an arbovirus from the genus Flavivirus in the family Flaviviridae, forms a nucleocapsid structure through interactions between its genome and multiple copies of the capsid protein. Experimental studies have confirmed the interaction between the viral capsid protein and lipid droplets, indicating a protein-lipid interaction. Cryo-EM studies show that in immature viruses, the nucleocapsid is located close to the viral membrane. This study uses multiple MD simulations to explore the orientation of the capsid protein relative to the lipid membrane, focusing on how the protein's hydrophobic pocket interacts with the membrane. We also investigated the interaction between the capsid protein and RNA, considering the effects of sequence length and identity. Finally, we construct a model of the lipid-protein-RNA complex, demonstrating that the capsid protein's hydrophobic pocket interacts with the membrane, while the positively charged H4 helix interacts with the negatively charged RNA. This research may identify crucial interactions for immature virus particle formation and provide insights for future therapeutic interventions.

Dengue Virus↗
PubMed2026

Virome of the Russian Grapevine Germplasm: A Final Study and Summary.

Ampelographic collections play an important role in the conservation of grapevine genetic resources and therefore require continuous phytosanitary monitoring. In this study, the virome of grapevines from the Magarach ampelographic collection in Russia was analyzed using total RNA high-throughput sequencing. A total of twenty-seven grapevine viruses and four viroids were identified. Two viruses were characterized as putative novel species: (+) ssRNA grapevine umbra-like virus 5 (GULV-5) and the bipartite (+) ssRNA grapevine Magarach secovirus (GMSV), which, together with related viruses, may represent a novel genus within the family Secoviridae. Among the economically important viruses, the most prevalent were grapevine fanleaf virus (76%), grapevine leafroll-associated virus 1 (39%), and grapevine virus A (33%). Mixed infections involving two or three of these viruses were detected in 50% of the analyzed grapevines. Grapevine virus D was detected in Russia for the first time. Phylogenetic analysis of 222 assembled virus and viroid genome sequences revealed high genetic diversity. The obtained results were summarized and compared with previous virome studies conducted on four Russian ampelographic collections.

RNA-Seq↗
PubMed1979

Effect of interferon on murine leukaemia virus infection. IV. Formation of non-infectious virus in chronically infected cells.

Interferon (150 units/ml) was used to treat SC-1 and AKR-2B cells which were chronically infected with murine leukaemia virus (MuLV). This led to a 100-fold decrease in the amount of infectious virus released into the medium and a 10-fold decrease in the number of virus particles measured by the virion-associated reverse transcriptase assay. However, there was little change in the amount of cell-associated infectious virus, though nearly twice as many cell-associated virions were counted in electron micrographs. With both types of cells, interferon blocked MuLV replication at the post-budding stage, but it did not change the morphology of the particles produced or their content of virion 70S RNA. Infectious virus assembled on the cell membranes of interferon-treated cells was less stable at 37 degrees C than that grown in the absence of interferon. Release of infectious virus from interferon-treated cells was not inhibited by actinomycin D or cycloheximide, though both agents inhibited virus production in controls. These results show that interferon inhibits MuLV replication through effects on virion assembly; these lead both to the formation of non-infectious particles and of fewer virions. Kinetic analysis further shows that interferon affects MuLV assembly rapidly and induction of an antiviral protein may not be required.

Cell Line↗
PubMed1977

Membrane-associated assembly of M13 phage in extracts of virus-infected Escherichia coli.

Assembly of coliphage M13 is known to occur as the viral DNA crosses the cytoplasmic membrane, shedding its virus-coded DNA unwinding protein and acquiring from the membrane approximately 2400 copies of the major coat protein. Conditions are described in which extracts of M13-infected E. coli and membranes prepared from such extracts will support virus assembly at a rate equivalent to that of intact cells. Extracts prepared from cells infected with temperature-sensitive M13 mutants in genes 1, 3, 4, or 5 are temperature-sensitive in this cell-free assembly reaction. Phage assembly in vitro requires magnesium and as yet an unidentified heat-stable cofactor of low molecular weight. The rate of virus assembly is approximately linear with respect to extract concentration over a 10(4)-fold range, consistent with the observation that the entire M13 assembly activity copurifies with the cell membrane fraction.

Cell Membrane↗
PubMedDate not supplied

Inhibition of herpes simplex virus multiplication by 2,3-bis(acetyl mercaptomethyl)-quinoxalin.

The drug 2,3-bis(acetyl mercaptomethyl)-quinoxalin (BAMMQ) was 99.9% inhibitory for herpes simplex virus (HSV) multiplication in cell cultures at concentrations of 1.6 X 10(-5) M or less. The drug was not inactivating for the virus, did not interfere with adsorption and penetration of the virus, and was still active when added as late as 12 h after infection with HSV. BAMMQ did not prevent HSV DNA replication, but interfered with a late stage of virus assembly and/or maturation.

Cell Line↗