Enhancement of reovirus infectivity by extracellular removal or alteration of the virus capsid by proteolytic enzymes.
TL;DR: The in vitro removal of the capsid layer by proteolytic enzymes resulted in an increase in infectivity in reovirus preparations, contributing to a better understanding of virus infection, stability and structure.
Abstract: Summary
Reovirus particles have an inner coat between the capsid and the nucleic acid core. The in vitro removal of the capsid layer by proteolytic enzymes resulted in an increase in infectivity in reovirus preparations. This finding contributes to a better understanding of virus infection, stability and structure, and helps explain results of kinetic studies of activation and inactivation. Further, the findings presented have practical application in the isolation and identification of reovirus, and in the preparation of high-titred virus stocks.
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TL;DR: A new model of Ad entry is proposed based on the present observations of capsid disassembly and membrane penetration, which possessed membrane lytic activity similar to partially disassembled virions.
Abstract: In contrast to enveloped viruses, the mechanisms involved in membrane penetration by nonenveloped viruses are not as well understood. In these studies, we determined the relationship between adenovirus (Ad) capsid disassembly and the development of membrane lytic activity. Exposure to low pH or heating induced conformational changes in wild-type Ad but not in temperature-sensitive Ad (ts1) particles that fail to escape the early endosome. Wild-type Ad but not ts1 particles permeabilized model membranes (liposomes) and facilitated the cytosolic delivery of a ribotoxin. Alterations in wild-type Ad capsids were associated with the exposure of a pH-independent membrane lytic factor. Unexpectedly, this factor was identified as protein VI, a 22-kDa cement protein located beneath the peripentonal hexons in the viral capsid. Recombinant protein VI and preprotein VI, but not a deletion mutant lacking an N-terminal amphipathic alpha-helix, possessed membrane lytic activity similar to partially disassembled virions. A new model of Ad entry is proposed based on our present observations of capsid disassembly and membrane penetration.
443 citations
Cites background from "Enhancement of reovirus infectivity..."
...During infection, these mature metastable virions undergo conformational changes in response to external stimuli, including binding to cell receptor (46), proteolytic digestion (42, 44), altered divalent cation concentrations (9, 22, 32), or acidification in endosomes (8, 30, 37)....
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TL;DR: A genetic approach has been used to define the molecular basis for the different patterns of virulence and central nervous system cell tropism exhibited by reovirus types 1 and 3 and it is determined that the S1 genome segment is responsible for the differing cell Tropism of reov virus serotypes and is the major determinant of neurovirulence.
Abstract: A genetic approach has been used to define the molecular basis for the different patterns of virulence and central nervous system cell tropism exhibited by reovirus types 1 and 3. Intracerebral inoculation of reovirus type 3 into newborn mice causes a necrotizing encephalitis (without ependymal damage) that is uniformly fatal. Animal inoculated with reovirus type 1 generally survive and may develop epedymal cell damage (without neuronal necrosis) and hydrocephalus. Using recombinant clones derived from crosses between reovirus types 1 and 3, we have been able to determine that the S1 genome segment is responsible for the differing cell tropism of reovirus serotypes and is the major determinant of neurovirulence. The type 1 S1 genome segment is responsible for ependymal damage with subsequent hydrocephalus; the type 3 S1 genome segment is responsible for neuronal necrosis and neurovirulence. We postulate that these differences are due to the specific interaction of the σ1 outer capsid polypeptide (the protein coded for by the S1 genome segment) with receptors on the surface of either ependymal cells or neuronal cells.
270 citations
245 citations
TL;DR: Recovery of the infectivity of L Sendai for L cells due to a direct enzymatic action of trypsin was demonstrated, showing that variations of Sendai virus in theinfectivity for L Cells and in the density are independent types of host-controlled modification.
Abstract: Sendai virus grown in fertile eggs (egg Sendai) infects L cells in which the synthesis of L Sendai (grown in L cells) occurs by the one-step mechanism. L Sendai is not infectious for L cells when tested by the tube titration method although it is infectious for chick embryos. When L cells infected with egg Sendai were dispersed by trypsin and plated on a monolayer culture of L cells, the viral agents spread to the adjacent recipient cells in which the synthesis of L Sendai occurred. The newly infected L cells became infectious for L cells again by trypsin treatment. Kinetic experiments suggested that the target of trypsin is the mature virus, of L Sendai nature, just budding from the L-cell surface. By using an immunofluorescent cell-counting technique, recovery of the infectivity of L Sendai for L cells due to a direct enzymatic action of trypsin was demonstrated. Under the optimal condition, the infectivity increased 1,000-fold for L cells and 10-fold for chick embryos, and both the titers could favorably be compared. No increasing effect of trypsin was observed on the infectivity of egg Sendai. Density centrifugation studies revealed a difference between egg Sendai and L Sendai in the density. Trypsin treatment which induced the maximal enhancement of L Sendai infectivity did not affect both the densities, showing that variations of Sendai virus in the infectivity for L cells and in the density are independent types of host-controlled modification.
197 citations
01 Jan 1985
TL;DR: It is anticipated that in the future concepts evolving from the field of virus, receptors will merge with those from other types of receptor interactions represented in this treatise.
Abstract: Publisher Summary Viral infection is initiated by attachment of the virus to the host cell. Viral adsorption to cells is mediated by a viral attachment protein that binds to a specific cell surface receptor. The viral attachment protein has been identified for many animal viruses. It has been established that receptor recognition is specific and can influence the host range of a virus. Details of the virus–cell interaction at the molecular level are beginning to emerge for myxoviruses and paramyxoviruses. This is because of major advances in the elucidation of the structure of the viral hemagglutinin, especially for influenza virus, to improved methods for the analysis of receptor specificity and insights into the mechanisms of viral penetration of cellular membranes. The value of elucidating the details of virus–host recognition probably goes far beyond understanding the host–parasite relationship. The factors relevant to viral recognition, attachment, and penetration are similar to those of the ligand–receptor and cell–cell interactions of higher organisms. Thus, it is anticipated that in the future concepts evolving from the field of virus, receptors will merge with those from other types of receptor interactions represented in this treatise.
184 citations
References
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194 citations
TL;DR: Purified reovirus particles contain a polymerase which transcribes virus-specific mRNA in vitro from the double-stranded, viral RNA genome, and the enzyme activity is markedly increased after heat-shocking the virions.
165 citations
TL;DR: Evidence is presented suggesting that progeny genomes are bound to site(s) possessing the fine structure of viral inclusions or factories, it appears that both the synthesis of single- and double-stranded viral RNA and the morphogenesis of progeny virus particles occur in such factories.
Abstract: Reovirus type 3 is phagocytized by L cells and rapidly sequestered inside lysosomes. Hydrolases within these organelles are capable of stripping the viral coat proteins, but they fail to degrade the double-stranded RNA genome. These observations support the view that sojourn of reovirus in lysosomes, when the lytic enzymes uncoat its genome, is an obligatory step in the sequence of infection. Although the mechanism for transferring the uncoated RNA out of lysosomes remains to be elucidated, evidence is presented suggesting that progeny genomes are bound to site(s) possessing the fine structure of viral inclusions or factories. It appears that both the synthesis of single- and double-stranded viral RNA and the morphogenesis of progeny virus particles occur in such factories.
147 citations
01 Jan 1965
TL;DR: In this paper, it was shown that about 14% of the parental label was finally transferred to foci where progeny virus was being formed, and the label was conserved in a macromolecular form throughout this period.
Abstract: Abstract Reovirus possesses an outer capsid and a subjacent shell, presumably necessitating the rupture of two separate protective coats to release the genome. This may occur intracellularly within phagocytic viral inclusions where whole particles are sequestered and gradually lose their coats. Cells infected with purified virus particles containing labeled RNA were sampled at intervals during a 12-hour experimental period, and then subjected to light and electron microscopic autoradiography. The label was conserved in a macromolecular form throughout this period. Because of asynchrony in the release of parental genomes and lack of identifiable, partially degraded forms of the virus outside the phagocytic inclusions, it was not possible to reconstruct the sequence of stages during the penetration of inoculum RNA to its site of function. However, about 14% of the parental label was finally transferred to foci where progeny virus was being formed. Evidence, derived from experiments with infected cells and tagging by means of Ferritin-antibody conjugates specific for reovirus protein, is presented which relates virus morphogenesis with the presence of mitotic-spindle tubules and a cytoplasmic filamentous component.
135 citations
TL;DR: Evidence, derived from experiments with infected cells and tagging by means of Ferritin-antibody conjugates specific for reovirus protein, is presented which relates virus morphogenesis with the presence of mitotic-spindle tubules and a cytoplasmic filamentous component.
131 citations