- Volume 57, Issue 1, 1981
Volume 57, Issue 1, 1981
- Review Article
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- Articles
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Announcement
International Course of Veterinary Clinical Immunology
Ecole Nationale Veterinaire D’Alfort (22–27 March 1982)
To provide a week intensive course in veterinary clinical immunology laboratory techniques
Closing date for registration: 30 January 1982
Information: Dept. of Microbiology and Immunology, Ecole Nationale Veterinaire D’Alfort, 7, Avenue du Général de Gaulle, 94704 Maisons Alfort Cedex Tel: (1).375.92.11. poste 245
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- Bacterial
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Proteus mirabilis Converting Phage 5006Mpα has an Oversized Genome
More LessSUMMARYProteus mirabilis phage 5006Mpa is a converting variant for ampicillin resistance of phage 5006M. We show here that the ampicillin resistance marker of transposon Tn1 is located on a 9.8% insertion with respect to the wild-type phage genome. This renders the 5006Mpa genome 5% oversized, albeit without loss of wild-type genetic material from the phage population.
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- Animal
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Characterization of Ribonucleotide Reductase Induction in BHK-21/C13 Syrian Hamster Cell Line Upon Infection by Herpes Simplex Virus (HSV)
More LessSUMMARYRibonucleotide reductase is an essential enzyme in mammalian DNA replication. In quiescent BHK-21/C13 cells exhibiting a low level of ribonucleotide reductase activity, infection with herpes simplex virus (HSV) resulted in the early induction of an altered ribonucleotide reductase. The extent of the induction was dependent upon the m.o.i. and could be diminished or prevented by u.v. treatment of the viral stock, or by inhibitors of mRNA synthesis or protein synthesis. The induction followed the same course of synthesis as viral thymidine kinase and DNA polymerase, and could thus be classified with them as a β polypeptide. These results suggested that the new activity was produced as a consequence of the virus genome expression. Comparisons of the properties of ribonucleotide reductase extracted from exponentially growing BHK-21/C13 cells showed that the HSV-induced enzyme differed from the cellular isozyme by its insensitivity to inhibition by dTTP, dATP or araATP and its resistance to high salt concentrations. On the other hand, the virus-induced enzyme and the cellular isozyme exhibited a similar sensitivity to hydroxyurea. Therefore, the reported inhibition of HSV DNA replication by hydroxyurea could be the result of inhibition of both HSV-induced and cellular reductase activities.
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Effect of 2-Deoxy-d-Glucose on Cytomegalovirus-induced DNA Synthesis in Human Fibroblasts
More LessSUMMARY2-Deoxy-d-glucose (dGlc) was found to selectively inhibit virus DNA synthesis in human embryonic lung cells infected with human cytomegalovirus (HCMV). The effective concentration of dGlc was approx. 10-fold higher in culture medium containing glucose instead of sodium pyruvate. This inhibitory action of dGlc was fully reversible following replacement of the inhibitor medium by fresh medium after a 48 h treatment of infected cells. Virus DNA synthesis could be selectively inhibited by addition of dGlc even after initiation of HCMV DNA replication. In contrast, virus DNA synthesis in herpes simplex virus-infected cells was insensitive to dGlc. The drug was found to deplete HCMV-infected cells of uridine triphosphate and caused a progressive reduction of uridine incorporation into RNA. To substantiate a possible interference by dGlc with the expression and/or function of virus-induced, chromatin-associated factors essential for virus DNA replication, DNA synthesis of chromatin preparations from dGlc-treated, HCMV-infected cells was analysed. In contrast to preparations of untreated or phosphonoacetic acid (PAA)-treated, HCMV-infected cells, those of dGlc-treated cells lacked significant in vitro DNA-synthesizing activity; virus DNA was not synthesized by these preparations. Tunicamycin in the presence of low concentrations of dimethyl sulphoxide was also found to be effective in abolishing HCMV-induced DNA replication. It is thus suggested that dGlc interferes with the function of an ‘early’ chromatin-associated glycoprotein essential for virus DNA synthesis.
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Host Cell-dependent Differences in the Oligosaccharide Moieties of the VSV G Protein
More LessSUMMARYThe oligosaccharide moieties of vesicular stomatitis virus glycoprotein from virus grown in four different cell lines have been characterized by sequential enzymic degradation followed by ion-exchange chromatography and analytical gel filtration. Whilst the same two peptide sites are glycosylated in all cell lines, the extent of sialylation of the oligosaccharides is, however, a function of the cell line in which the virus is produced. Using specific purified glycosidases for sequential degradation of glycopeptides obtained after Pronase digestion, the oligosaccharide structures from the different host cell lines appear similar. However, differential sensitivity of the glycopeptides to treatment with a partially purified mixture of endo- and exoglycosidases indicates that the oligosaccharide structures are not identical.
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Early Interaction between Mouse Hepatitis Virus 3 and Cells
More LessSUMMARYThe interaction between mouse hepatitis virus 3 (MHV3) and cells was studied in order to investigate whether or not early events occurring after infection could be involved in the difference in virus replication seen between mouse strains with different genetic sensitivities to MHV3 infection. Kinetic data showed that MHV3 uptake by both macrophages and L cells was time- and temperature-dependent. In addition, treatment of cells with cytochalasin B or prostaglandin E1, prior to virus infection, resulted in a strong inhibition of sheep red blood cell phagocytosis without any effect on MHV3 uptake. Similar uptake of radiolabelled MHV3 was shown by whole spleen cells, purified T lymphocytes and thymocytes. Furthermore, no difference in 3H-labelled MHV3 uptake was seen between macrophages originating from resistant A/J mice, semi-susceptible (C57B1/6 × A/J)F1 and susceptible animals. These results indicate, therefore, that genetically related in vivo sensitivity toward MHV3 infection is not related to differential uptake of virus by cells.
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Ecotropic and Xenotropic Type C Retroviruses Associated with Reticulum Cell Neoplasms of SJL/J Mice
More LessSUMMARYAn ecotropic type C retrovirus (D1-MuLV) isolated from SJL/J mice was injected into neonatally thymectomized SJL/J mice. There was no acceleration of development of reticulum cell neoplasm (RCN) in these mice as compared with the control, uninoculated but similarly thymectomized group. The incidence of RCN at 10 and 11 months after injection was 14.6% and 12.5% respectively. Two female mice inoculated with D1-MuLV developed mammary adenocarcinoma. There was persistence of high titres of the ecotropic virus associated with RCN and mammary tumour of SJL/J mice. Xenotropic virus (X-MuLV) was detected in spleens of normal SJL/J mice at ages 6 and 12 months (60% and 80% respectively) but not at other ages. The X-MuLV isolated from SJL/J mouse embryo cell cultures treated with 5-iodo-2′-deoxyuridine (SJL-MEF-X-MuLV) and that isolated from a spontaneous RCN (SJL-RCN-X-MuLV) were compared with NZB-X-MuLV (NZB mouse origin) and AT124-X-MuLV (NIH Swiss mouse origin) in regard to their host range, ion and primer-template preference by reverse transcriptase, virus interference and neutralization characteristics. Cross-neutralization and gp70 competitive radio-immunoassays showed that D1-MuLV is more closely related to AKR-MuLV than to Rauscher-MuLV and appears to share some virus envelope antigens with SJL-X-MuLVs. The type-specific gag gene product (p12) from Balb:virus-2 and NZB-X-MuLV was used in competitive radioimmunoassay, and SJL-RCN-X-MuLV was found to be more closely related to Balb:virus-2 (MuLV-Xα) than to NZB-X-MuLV (MuLV-Xβ).
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Immunological Characterization of a Mammary Tumour Virus from Swiss Mice: Multiple Epitopes Associated with the Viral Gene Products
More LessSUMMARYThe major antigens of a mouse mammary tumour virus (MMTV) isolated from the milk of exogenously infected MB+ Swiss mice were compared with the viral components of other MMTV strains by using the methodology developed by Teramoto et al., (1977a). The anti-gp47 (Swiss) serum differentiated between type- and group-specific antigenic determinants on the major glycoprotein; two distinct type-reactivities were demonstrated, one of them being shared by the MMTVs (Swiss) and (RIII), and the other by the MMTVs (C3H) and (GR). The MMTVs (Swiss) and (RIII) also reacted identically in a ‘type-specific’ assay using an anti-p28 (Swiss) serum, but a distinct reactivity was observed with the MMTV (C3H). In the isologous test where an anti-(total RIII) serum was used to bind intact, externally labelled RIII virions, the Swiss virus was seen to possess a type-specific determinant on its surface which distinguished itself from both MMTVs (RIII) and (C3H). The Swiss/fC57BL mice (which are devoid of the milk virus and for this reason are referred to as MB−), expressed only the internal virus antigens in their mammary glands. Under the ‘type-specific’ assay conditions, the p28 antigen present in the mammary gland extracts of the MB+ mice was indistinguishable from the p28 antigen purified from the Swiss virion, but was clearly distinct from the p28 reactivity present in the mammary gland extracts of the MB− mice. The p28 (MB−) antigen may thus represent the expression of an endogenous virus sequence different from the milk virus genome.
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Variety of Endogenous Proviruses in the Genomes of Chickens of Different Breeds
More LessSUMMARYWe have compared endogenous proviruses in DNA of chickens of 11 breeds by means of Southern’s technique. Many of the endogenous virus loci found were missing from the genomes of the extensively studied white leghorn chickens, although some of the proviruses and especially ev-1 appeared to be widely spread among different chickens. Most of the proviruses were similar to Rous-associated virus (RAV-O) as judged by the EcoRI digestion patterns. Several genetically different proviruses were found in the DNA of 28 brown leghorns. They contain neither ev-1 provirus in their genome, nor any other one common for all individuals. All four Italian partridge-coloured chickens examined appeared to be free from ALV-related sequences in their DNA showing the possibility of normal life without known endogenous proviruses. Possible causes of inter-breed differences of chicken endogenous proviruses are discussed.
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Detection of Hepatitis B Virus-specific DNA in the Genomes of Human Hepatocellular Carcinoma and Liver Cirrhosis Tissues
More LessSUMMARYHepatitis B virus-related DNA was detected in the chromosomal DNA of three out of seven hepatocellular carcinomas and two out of five cirrhosis samples examined, by means of the blot-hybridization technique, described by Southern (1975). The integration patterns were not identical but some similarities raise the question of whether there are some preferred sites of viral integration.
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Mapping Temperature-sensitive Mutants of Vesicular Stomatitis Virus by RNA Heteroduplex Formation
More LessSUMMARYDuplex RNA molecules made by hybridization of virion and mRNA of vesicular stomatitis virus (VSV) were digested with ribonuclease and separated into five size classes, each containing the gene and the mRNA for one of the VSV proteins. Denaturation of the duplexes yielded full size mRNA lacking poly(A) tails. Utilizing duplex formation between the RNAs from VSV temperature-sensitive (ts) mutants and their revertants and subsequent RNase digestion under varying salt conditions, specific cleavages within a certain duplex were seen for representative mutants from complementation groups III, IV and V. Specific cleavages were not seen for a group II mutant. From these results gene assignments cannot be made for group II; equivocal assignments are made for group III and clear assignments made for group IV and V. The assignment for the group V mutants, however, does not conform to expectations. Nevertheless, from these studies and other published ones, there is the suggestion that interactions may exist between the gene products of complementation groups II and V during VSV transcription and morphogenesis. These results also support the lack of transcriptional splicing for VSV mRNAs.
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Antibody-dependent Enhancement of Plaque Formation on Cell Lines of Macrophage Origin – A Sensitive Assay for Antiviral Antibody
More LessSUMMARYAn assay for antiviral antibody based on antibody-dependent plaque enhancement (ADPE) in the macrophage cell line P388D1 is described which is as sensitive as, or more sensitive than a radioimmune assay. The method is applicable to a range of Togaviridae and Bunyaviridae although not to Picornaviridae and Herpesviridae. The variables affecting the assay are investigated.
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Orbiviruses and Bunyaviruses from a Seabird Colony in Scotland
More LessSUMMARYViruses isolated from ticks (Ixodes uriae) and a kittiwake (Rissa tridactyla) from a seabird colony at St. Abb’s Head, Scotland, were shown by complement fixation tests (CFT) to be antigenically related to the Uukuniemi and Kemerovo serogroups. Electron microscopic examination of cell cultures infected with the Kemerovo group viruses revealed particles characteristic of orbiviruses, 72 ± 3 nm in diam., with an inner core 37 ± 3 nm in diam., in association with intracytoplasmic, densely staining granular areas, and with fibrillar and tubular structures. Cell cultures infected with the Uukuniemi group viruses revealed characteristic bunyavirus particles, 94 ± 7 nm in diam., with a closely adherent envelope. Both orbi- and bunyaviruses were isolated from two tick pools and the kittiwake. A third tick pool contained an orbivirus which cross-reacted with the other isolates in CFT and fluorescent antibody tests, but was distinguished from them by neutralization tests.
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Neonatal Infection with Mouse Thymic Virus: Spleen and Lymph Node Necrosis
More LessSUMMARYMouse thymic virus (TA) is a naturally occurring herpesvirus of laboratory and wild mice, which produces massive thymic necrosis when inoculated into newborn mice. Our histopathological study showed necrosis not only of the thymus but also of the spleen and lymph nodes which was noticeable by day 7 and complete by day 14. Both spleen and lymph nodes regenerated to an almost normal histological pattern by day 70. The results show that TA infects multiple lymphoid tissues causing massive necrosis in all, and is not limited to a single site, the thymus. TA infection was found to be a persistent herpesvirus infection in both the lymph nodes and spleen. During the period of acute infection, as necrosis increased, the response of cell suspensions of lymph nodes to the T cell mitogens concanavalin A and phytohaemagglutinin was virtually non-existent. Activity returned to normal as the histological repair progressed.
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Human Cytomegalovirus-associated DNA Polymerase and Protein Kinase Activities
More LessSUMMARYHuman cytomegalovirus (HCMV), purified exclusively from the extracellular media, contained a DNA polymerase activity in addition to a protein kinase activity. The DNA polymerase expressed its maximum activity in the presence of 5 to 10 mm-MgCl2. The enzyme was able to use effectively activated calf thymus DNA, poly(dA).oligo(dT)12–18 and poly(dC).oligo(dG)12–18 as the template primers. The DNA polymerizing activity was eluted with 0.18 to 0.2 m-KCl from a phosphocellulose column. It was relatively resistant to phosphonoacetic acid inhibition even at a high concentration of 100 µg/ml with activated calf thymus DNA as the template primer, but the DNA polymerase activity was totally suppressed at this concentration when poly(dA).oligo(dT)12–18 was used as the template primer. The enzyme activity was inhibited by ammonium sulphate at 0.01 to 0.3 m with either activated calf thymus DNA or poly(dA).oligo(dT)12–18 as the template primer. The protein kinase has maximum activity in the presence of 10 to 20 mm-MgCl2, and preferred virion proteins as phospho-acceptor to protamine sulphate. Histone, caesin and bovine serum albumin (BSA) were found to be poor substrates. The phosphorylated protein pattern of the in vivo [32P]orthophosphate-labelled virions was not identical to that of the in vitro phosphorylated Nonidet P40-dissociated virions, although seven phosphorylated polypeptides did co-migrate in SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Procedures known to solubilize virions showed that the DNA polymerase and protein kinase were internal components of the virion.
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A Rabies Virus Persistent Infection in BHK21 Cells
More LessSUMMARYA rabies virus persistent infection in BHK21 S13 cells was established and maintained in culture for more than 4 years. Initially, the cultures produced a large plaque virus similar to that produced by the original virus, but between the 10th and 20th passage, this was replaced by a small plaque variant. By the 200th passage, infectious virus could no longer be detected in the medium. After further cell passages (⩾ 300) no infectious particles could be detected in the medium. At various passage levels, the persistently infected cells were labelled with [35S]methionine and the virus antigens immunoprecipitated and analysed by polyacrylamide gel electrophoresis. No changes in the virus polypeptides were observed in the establishment of the persistent state. However, after the 20th passage (predominance of small plaque variant) there was an increase in the size of the glycoprotein. This was followed (164th passage) by a change in the M1 polypeptide which was subsequently further modified in the defective state (⩾ 300 passages). Virus isolated from the 400th passage by treatment of the cells with DEAE-dextran, was also modified in the glycoprotein and M1 polypeptides and contained less L polypeptide than the original virus. This virus grew more slowly, to a lower titre and was no longer pathogenic in suckling mice.
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Differentiation of Measles Virus Strains and a Strain of Canine Distemper Virus by Monoclonal Antibodies
More LessSUMMARYMonoclonal antibodies raised against the Hallé strain of measles virus were tested for their strain specificity using other measles virus isolates (Edmonston, Leningrad, Lec and two fresh isolates JT and Fasquelle). Monoclonal antibodies to L, HA and NP polypeptides, with one exception, reacted with all the measles virus strains tested; antibody from hybrid line 25 failed to react with the NP polypeptide of JT virus by immunofluorescence or radioimmunoprecipitation. Three other monoclonal antibodies, two reacting with NP and one with HA, although giving a positive immunofluorescence reaction, did not immunoprecipitate labelled antigen from JT virus-infected cells. The immunological relationship of canine distemper and measles viruses was also investigated with monoclonal antibodies. Two of the three anti-NP and three of the four anti-HA monoclonal antibodies reacted with canine distemper virus in an immunofluorescence reaction but only one (anti-NP) reacted in a radioimmunoprecipitation test.
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Phosphorylation of Influenza Virus Nucleoprotein in vivo
More LessSUMMARYTwo-dimensional analysis of polypeptides from A/FPV/Rostock/34 (FP/R)-infected chick embryo fibroblast cells using non-equilibrium pH gradient gel electrophoresis followed by polyacrylamide gel electrophoresis, showed that nucleoprotein (NP) was the only detectable virus phosphorprotein and was present in both the nucleus and cytoplasm. The kinetics of accumulation of phosphorylated NP in the nucleus and cytoplasm were similar, suggesting that the presence or absence of phosphate groups did not control the entry of NP into the nucleus. In the course of this study, two-dimensional analysis of [35S]methionine-labelled FP/R-infected cells revealed some major differences from previously published work which are discussed.
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Persistent and Lytic Infections with SSPE Virus: A Comparison of the Synthesis of Virus-specific Polypeptides
More LessSUMMARYThe synthesis of virus-specific polypeptides and messenger RNA in cell cultures persistently infected with an isolate of measles virus from a patient with subacute sclerosing panencephalitis (SSPE) has been compared to that found in a lytic infection with the homologous virus. The persistent infection described here was chosen as its biological characteristics reflect those of virus-infected brain cells from SSPE patients. The synthesis of H, N and possibly F protein was seen in both lytic and persistent infections, but the synthesis of M protein was only detected in the lytic infection. However, messenger RNA isolated from either the lytic or persistent infection directed the synthesis in a cell-free translation system of all structural polypeptides, including M, and also three non-structural polypeptides, with mol. wt. of 34000, 30000 and 18000. Messenger RNAs coding for the virus-specific polypeptides were also shown to be polyadenylated. In addition, those polypeptides made in vitro which were antigenically related to the haemagglutinin, demonstrated structural changes after passage through a persistent infection.
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Detection of Entomopoxvirus Proteins in Insect Cell Culture by Enzyme-linked Immunosorbent Assay (ELISA)
More LessSUMMARYAn indirect enzyme-linked immunosorbent assay (ELISA), using antibodies made against gradient-purified Amsacta moorei entomopoxvirus (EPV), detected down to 13 ng of virus protein. Little antigenic relatedness was detected by ELISA between the structural proteins of Amsacta EPV, Euxoa EPV, Melanoplus EPV and vaccinia virus. Antibodies made against Amsacta EPV occlusion body matrix protein cross-reacted extensively with the occlusion body protein of Euxoa EPV. A rapid increase in the biosynthesis of Amsacta EPV structural proteins in Estigmene acrea (BTI-EAA) cells was detected from 12 to 50 h after virus infection. Low concentrations of virus-specific proteins were detected by ELISA in extracts of Amsacta EPV-infected Trichoplusia ni (Tn-368) cells from 1 to 96 h after virus inoculation.
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Flow Cytometric Analysis of DNA Content of Mouse Liver Cells Following in vivo Infection by Human Adenovirus Type 5
More LessSUMMARYHuman adenovirus type 5 caused acute hepatocellular damage when injected intravenously into C57B1/6 mice. Early protein (P) and late virus protein (V) antigen staining by immunofluorescence was located principally, if not exclusively, in hepatocytes. Autoradiography following incorporation of tritiated thymidine into Ad5-infected liver cells in vivo indicated that DNA synthesis was initiated in hepatocytes. Flow cytometry showed that cells with a 4n DNA content prior to infection were highly susceptible to infection, with 75% being lost from the liver cell population by 5 days post-infection. This observation was correlated with the observed pathology during the course of the infection.
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Mechanisms of Early and Late Polykaryocytosis Induced by the Bovine Leukaemia Virus
More LessSUMMARYSyncytia formation induced by the bovine leukaemia virus (BLV) has been classified as ‘early’ or ‘late’ polykaryocytosis. Early polykaryocytosis arises in the first 24 h in mixed cultures of BLV-infected cells with indicator cells. Late polykaryocytosis is observed 4 to 8 days after infection of sensitive cells with cell-free infectious BLV. Our results demonstrate that the two phenomena proceed from different mechanisms. Late polykaryocytosis results from an active process dependent on the integrity of the virus genome. In contrast, early polykaryocytosis is a passive process which does not require any de novo virus synthesis but is dependent on the presence of virus proteins in inducer cells.
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Comparison of the Antiviral Activities of Various Cloned Human Interferon-α Subtypes in Mammalian Cell Cultures
More LessSUMMARYFive human interferon-α (leukocyte) subtypes derived from genes cloned in Escherichia coli have been compared for their ability to induce antiviral activity against vesicular stomatitis virus infection of various mammalian cell cultures. These interferons, designated LeIF-A (IFN-α 2), -B, -C, -D (IFN-α 1) and LeIF-F, show different relative activities when assayed on human, bovine, hamster, mouse, rabbit and monkey cell lines. As with a natural human buffy-coat interferon-α preparation, three subtypes (LeIF-B, -C and -D) showed considerable activity on RK-13 rabbit cells, but two (LeIF-D and -F) also showed some activity on mouse L-929 cells. Of the five interferon subtypes examined, LeIF-F demonstrated the highest degree of species specificity.
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The Interaction of Encephalomyocarditis Virus with its Erythrocyte Receptor on Affinity Chromatography Columns
More LessSUMMARYGlycophorin, the major sialoglycoprotein in the human erythrocyte surface membrane, can serve as a red cell receptor for both wheat-germ agglutinin (WGA) and encephalomyocarditis (EMC) virus since glycophorin bound to WGA–Sepharose can at the same time bind EMC virus. In contrast, glycophorin bound to WGA–Sepharose cannot bind EMC virus in the presence of SDS. The evidence suggests that virus binding to glycophorin-WGA–Sepharose occurred in the absence of SDS because glycophorin was present in aggregated complexes which were large enough either to accommodate both EMC virus and WGA at the same time, or alternatively to provide sufficient attachment sites for multivalent binding of virions.
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Analysis of Deoxycytidine (dC) Deaminase Activity in Herpes Simplex Virus-infected or HSV TK-transformed Cells: Association with Mycoplasma Contamination but Not with Virus Infection
More LessSUMMARYDeoxycytidine (dC) deaminase activity has been previously reported to be induced in herpes simplex virus (HSV)-infected cells (Chan, 1977). In contrast, we report here that HSV infection of either hamster cells naturally deficient in this enzyme activity or mouse cells containing a low level of activity never resulted in appearance or stimulation of dC deaminase, whereas thymidine kinase (TK) was always induced. Surprisingly, dC deaminase activity, which differed by electrophoretic mobility from the mouse or human cell enzyme, was discovered in some cells selected for the presence of HSV TK after infection with u.v.-irradiated HSV. Evidence is presented which suggests that the appearance of this new enzyme was not due to the presence of virus genes but rather to mycoplasma contamination.
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- Plant
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In vitro Transcription of Double-stranded RNA by Virion-associated RNA Polymerases of Viruses from Gaeumannomyces graminis
More LessSUMMARYSeveral double-stranded (ds) RNA Gaeumannomyces graminis viruses in groups I and II, but none in group III, have been shown to possess virion-associated RNA polymerase activity. The products of polymerase reaction were full-length single-stranded (ss) RNA transcripts of one of the strands of each of the dsRNA genome segments. Synthesis of ssRNA in vitro continued for up to 48 h during which, on average, up to eight full-length transcripts were produced per dsRNA molecule, i.e. reinitiation of transcription occurred in the in vitro system. In reactions containing [3H]UTP, label was also incorporated into all the dsRNA genome segments, reaching a maximum after 8 h. Examination of transcribing particles by electron microscopy revealed the presence of particles showing the release of looped ssRNA molecules, both ends of which were attached to the particle, as well as particles with one or two linear RNA strands attached. The modal length of the single linear RNA strands was within the range expected for full-length transcripts of the genome dsRNA segments.
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Polar Assembly of Clover Yellow Mosaic Virus
More LessSUMMARYClover yellow mosaic virus (CYMV) protein encapsidates its RNA at pH 7.5, low ionic strength and at a temperature of 25 °C. Protected RNA fragments extracted from the initiation complexes contained the cap structure m7GpppGp in the stoichiometric proportions expected for fragment sizes. These results were consistent with the location of the initiation site for assembly at or near the 5′ end of RNA; consequently, the maturation process is polar (5′ to 3′ direction). This strengthens the case for polar initiation as an alternative to internal initiation in the assembly of helical plant viruses.
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Luteovirus-like Particles Associated with Subterranean Clover Red Leaf Virus Infection
More LessSUMMARYSmall isometric virus-like particles have been detected in thin sections of phloem transfer cells of subterranean clover plants infected with subterranean clover red leaf virus (SCRLV). Virus-like particles similar in size and appearance but serologically distinct from those of potato leafroll virus, were also detected in purified preparations from SCRLV-infected plants. The morphology of the particles and their distribution in infected cells is consistent with SCRLV being a member of the luteovirus group, as previously suggested by its biological properties.
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- Corrigendum
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