- Volume 68, Issue 11, 1987
Volume 68, Issue 11, 1987
- Review Article
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The Mutation Rate and Variability of Eukaryotic Viruses: An Analytical Review
More LessPerhaps the most important factor to limit the effectiveness of vaccines against virus infections is that of virus variation. Successful vaccines have been developed against viruses such as those causing smallpox, measles, yellow fever and poliomyelitis, and they are effective against most circulating virus strains. However, with some viruses vaccination has been much less successful either because numerous antigenically distinct strains co-circulate, as is the case for rhinoviruses, or because new strains are continually emerging, as in the case of influenza virus. Despite the importance of virus variability, little is known about the factors that influence it and that are responsible for the dramatically different patterns of variation displayed by different viruses. The primary source of variation is obviously mutation, and it has been suggested in several recent papers that the extreme variability of some viruses may be a consequence of an unusually high rate of mutation (Holland et al., 1982; Reanney, 1984; Domingo et al., 1985; Saitou & Nei, 1986). The purpose of this analytical review is to summarize recent information about the mutation rates of eukaryotic viruses, and to discuss the relationship between such rates and virus variability in the field.
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- Bacterial
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A Physical Analysis of the Prophage of Proteus mirabilis PM5006
More LessSummaryProteus mirabilis phage 5006M was investigated as a prophage by DNA hybridization. A physical map of the prophage was established and the site of integration was localized on the phage genome. Older reports that the phage is cryptic in P. mirabilis could not be verified.
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- Animal
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Antigenic Mapping of the Surface Proteins of Infectious Hepatitis B Virus Particles
More LessSummaryTo identify further the surface proteins of the native virus, hepatitis B virus (HBV) particles purified from HBe antigen (Ag)-positive human sera were used as immunogens to produce murine monoclonal antibody (MAb)-secreting hybridomas. The specific binding of antibodies to the HBV envelope (env) proteins was determined in indirect radioimmunoassay and by Western blot analysis. Six MAbs directed against major hepatitis B surface antigen (HBsAg) recognized conformational epitopes on S proteins (P24s/GP27s). Three preS2-specific MAbs reacted with the middle env proteins (GP33s/GP36s) in the 22 nm HBsAg spherical particles. One MAb, F222, was found to react specifically with the two very large (VL) HBV surface proteins with M r 54K and 66K. The epitope recognized by F222 was located on the protruding N terminus which, in the assembled virus particles, was readily split off by trypsin or V8 protease treatment. The presence of these VL proteins appeared to correspond to the presence of the large env proteins (P39s/GP42s). The data described here indicate that F222 probably recognized an assembled topographic site which could be involved in virus entry into hepatocytes. Moreover, our results suggest that the preS-coded part of the HBV env proteins, which is sensitive to proteases in vitro, could be unstable in vivo and stabilized by immunoglobulins.
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Isolation and Characterization of Monoclonal Antibodies to Simian Virus 5 and Their Use in Revealing Antigenic Differences between Human, Canine and Simian Isolates
More LessSummaryHybridomas secreting monoclonal antibodies to simian virus 5 (SV5) were obtained following immunization of mice with purified preparations of a human isolate (LN) of SV5. Immune precipitation studies showed that these monoclonal antibodies had specificities for the haemagglutinin-neuraminidase (HN), fusion (F), nucleo-, matrix and phospho- (P) proteins of SV5. By use of a radioimmune competition assay the monoclonal antibodies to the HN protein were assigned to four groups, members of which recognized different antigenic sites on the protein. All the anti-HN antibodies and the anti-F antibody neutralized virus infectivity. The 54 monoclonal antibodies obtained were used to determine whether there were antigenic differences between five human, two canine and one simian isolate of SV5. Although most of the monoclonal antibodies reacted with all isolates, a few did reveal antigenic differences in the HN, F and P proteins. Furthermore, analysis by SDS-PAGE showed that while the electrophoretic mobilities of most of the virus polypeptides of these isolates were similar some differences could be detected. In particular the P protein showed the most marked mobility differences between the human, canine and simian isolates. Slight differences in the mobility of the F1 glycoprotein could also be visualized.
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Strain Variation of Respiratory Syncytial Virus
More LessWestern blotting and immunoperoxidase staining with monoclonal antibodies were employed to analyse epitopic and polypepide molecular weight variation among isolates of respiratory syncytial (RS) virus collected in Newcastle between 1965 and 1986. One group of isolates resembled the A2 and Long prototype subgroup A strains of RS virus in possessing a P protein of M r 34000. Isolates in this subgroup showed two patterns of reactivity with subgroup A-specific monoclonal antibodies to the G glycoprotein and 22K protein. Isolates with both reactivity patterns were isolated throughout the period studied. Isolates in the second group resembled the 8/60 subgroup B prototype strain in their lack of reactivity to subgroup A-specific monoclonal antibodies but were heterogeneous in P protein molecular weight. The earliest isolate only, made in 1965, possessed a P protein of Mr 31000 resembling the prototype strain. All subsequent subgroup B isolates possessed a higher M r, 33000, P protein. Overall, subgroup A viruses were isolated most frequently although subgroup B strains may have predominated in some epidemics.
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Molecular Cloning and Sequencing of the F and 22K Membrane Protein Genes of the RSS-2 Strain of Respiratory Syncytial Virus
More LessSummaryThe nucleotide sequences of the adjacent genes coding for the F protein and 22K protein of the RSS-2 strain of human respiratory syncytial (RS) virus were determined from cDNA clones of genomic RNA. Comparison of these sequences and the inferred amino acid sequences of the F and 22K proteins with the corresponding published sequences of another subgroup A virus, the A2 strain of RS virus, reveals extensive overall homology (>95%) at both the nucleotide and amino acid levels, even though these two viruses were isolated 15 years apart in different continents. The intergenic region and the hydrophobic amino-terminal signal sequence of the F proteins of the two viruses, however, are much less conserved.
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Structure and Mapping of the DNA of Human Parvovirus B19
More LessSummaryDNA from human parvovirus B19 was prepared from infected serum and examined by electron microscopy. Double-stranded molecules were seen, often with characteristic ‘fold-back’ ends that were assumed to be due to the inverted terminal repeats of the genome DNA. This double-stranded DNA was mapped with 13 restriction enzymes. More than 40 isolates, including the virus from the original B19 serum, were compared. Although isolates could be grouped by this method, there was no correlation between a particular restriction endonuclease map and any of the several disease presentations of the virus.
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Genome Analysis and Reverse Transcriptase Activity of Human Teratocarcinoma-derived Retroviruses
More LessSummaryFive of five human teratocarcinomas cultured in vitro could be induced to synthesize retrovirus-like particles, albeit in extremely low amounts. The accumulation and purification of the human teratocarcinoma-derived retrovirus (HTDV) from one of these cell lines allowed characterization of its genomic material as high mol. wt. (60S) RNA. Partial purification of HTDV-associated RNA-dependent DNA polymerase (reverse transcriptase) has also been achieved. HTDVs are easily distinguishable from the exogenous human T-lymphotropic viruses and human immunodeficiency viruses by morphological, biological and immunological criteria.
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Evidence that Deletion of Coding Sequences in the 5′ End of the Thymidine Kinase Gene of Herpes Simplex Virus Type 1 Affects the Stability of the Gene Products
More LessSummaryThe experiments described in the present work were designed to study the function of the N-terminal end of thymidine kinase (TK) encoded by herpes simplex virus type 1. Specifically we were interested to know whether this end was involved in binding of the enzyme to other molecules, had any influence on its subcellular localization or affected one or more of the activities associated with the enzyme. A parental enzyme and a deletion mutant, lacking the 45 N-terminal amino acids, derived from this strain, were used. Thymidine kinase from the parental virus bound to DNA-Sepharose, but the truncated enzyme did not. This was apparently not due to a specific ability to bind to DNA, since immunofluorescence studies indicated that both the normal and the deleted TK were mainly located in the cytoplasm, preferentially in the perinuclear region. Phosphorylation of thymidine as well as the amounts of TK polypeptides were markedly reduced at late times after infection with the mutant, but not to the same extent after infection with the wild-type. The deleted TK gene was efficiently transcribed as shown by hybridization of RNA to a probe specific for the gene, and this RNA directed the synthesis in vitro of TK polypeptides. Deletion of the 5′ end of the gene seems to affect the stability of either the enzyme or TK-specific mRNA, or both.
The TMP phosphorylating activity seems to be particularly destabilized relative to the thymidine phosphorylating activity.
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Augmentation of Natural Immune Defence Mechanisms and Therapeutic Potential of a Mismatched Double-stranded Polynucleotide in Cutaneous Herpes Simplex Virus Type 2 Infection
More LessSummaryWe studied the effect of an analogue of polyinosinic acid: polycytidylic acid, the mismatched poly(rI).poly(rC12U), on herpes simplex virus type 2 (HSV-2)-induced cutaneous disease in the guinea-pig. Recurrence patterns and HSV-2-induced immune responses were also defined. Intranasal administration (l·5 μg/g body weight, five doses at 48 h intervals) of poly(rl). poly(rC 12U) during initial HSV-2 infection caused a significant (P < 0·05) reduction in virus titres in the skin and decreased (P < 0·01) the duration and severity of the primary cutaneous lesions. The incidence and frequency of subsequent recurrent episodes were also significantly (P < 0·01) reduced. Titres of serum neutralizing antibody were identical in treated and untreated animals. Interferon (IFN) activity was detectable in the sera from poly(rl). poly(rC12U)-treated animals. Peripheral blood mononuclear (PBL) and spleen cells from treated animals had enhanced cytotoxic activity for HSV-2-infected and uninfected target cells. The cytotoxic activity of the PBL was enhanced by treatment in vitro with poly(rl). poly- (rC12U) or IFN.
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Resistance to Methylation de novo of the Human Cytomegalovirus Immediate Early Enhancer in a Model for Virus Latency and Reactivation in vitro
More LessSummaryRat-9G cells carry several stably integrated copies of the major immediate early (IE) transcription unit of the human cytomegalovirus (HCMV). In these cells IE expression is repressed but inducible. In this report we describe the DNA methylation status of HpaII, HhaI and AhaII sites within the IE gene, determined at different passage levels. Most, if not all, of the resident IE genes were progressively methylated in a similar fashion. This resulted in DNA methylation patterns in which sites surrounding the IE upstream region were preferentially methylated to a high degree. In contrast, sites within the 19 bp IE enhancer elements were markedly under-methylated. This particular DNA methylation pattern probably resulted from differences in DNA methylation rates, sites within the IE enhancer being methylated at only a very low rate. Methylation of the IE genes did not affect their inducibility, which might be related to the very low methylation level of the IE enhancer.
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New Type B Isolates of Epstein—Barr Virus from Burkitt’s Lymphoma and from Normal Individuals in Endemic Areas
SummaryAll Epstein-Barr virus (EBV) isolates can be classified as type A or type B depending upon the identity of their EBV nuclear antigen (EBNA) 2 protein. The great majority of isolates examined to date encode an EBNA 2A protein like that of the reference type A strain B95-8. Type B virus strains, encoding an antigenically distinct EBNA 2B protein, have as yet only been rescued from rare Burkitt’s lymphoma (BL) cell lines of African origin (Jijoye, AG876). Our recent finding that type B isolates are less efficient than type A in in vitro transformation assays prompted us to determine (i) the relative contribution the two types of virus make to the incidence of BL in endemic areas of Africa (Kenya) and New Guinea and (ii) the relative incidence of infection with these two types in the normal population in these same areas. On the first point, EBNA 2 gene typing using specific DNA probes showed that four of ten recently established Kenyan BL cell lines and two of four BL cell lines from New Guinea carried type B virus isolates. To address the second point, spontaneous lymphoblastoid cell lines were established from the blood of normal virus carriers and typed for EBNA 2 at the protein level; a significant proportion (> 20 %) of the normal population in both the above BL- endemic areas were infected with type B isolates. This is the first indication of the widespread nature of type B virus infection in any community and the first isolation of such viruses from a non-BL source. The reproducible size of the EBNA 2B protein encoded by all type B isolates irrespective of their geographical origin, and of the EBNA 1 protein encoded by all type B isolates from one area, contrasted markedly with the extreme variability in the size both of EBNA 2A and of EBNA 1 seen generally among type A isolates. This suggests that the number of type B virus strains in existence worldwide could be quite limited. Most importantly, the data suggest that type B viruses, despite their relatively poor performance in in vitro transformation assays, can contribute at least as efficiently as can type A viruses to the pathogenesis of BL.
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Structural Proteins of Bovine Coronavirus and Their Intracellular Processing
More LessSummaryThe Quebec isolate of bovine coronavirus (BCV) was found to contain four unique major structural proteins. These proteins consisted of the peplomeric protein (gp190/E2, gp100/E2), the nucleocapsid protein (p53/N) and its apparent trimer (p160/N), a family of small matrix glycoproteins (gp26/El, gp25/El and p23/El) and the putative haemagglutinin (gpl24/E3). Pulse-chase experiments utilizing polyclonal antiserum and monoclonal antibodies indicated that the unique BCV E3 protein had as its primary precursor an A-linked glycoprotein with an M r of 59000 (gp59) which underwent rapid dimerization by disulphide bond formation to yield gp118. Further glycosylation of gp118 produced gp124/E3 which incorporated fucose. Thus gp124/E3 was probably a homodimer. The processing of the E2 and E1 proteins of BCV was similar to that shown previously for mouse hepatitis virus. A large AM inked precursor glycoprotein, gpl70, underwent further glycosylation to yield gp190/E2 before subsequent proteolytic cleavage to yield gp100/E2. The glycosylated El (gp26, gp25) proteins arose as a result of O-linked glycosylation of p23/El as indicated by the resistance of these species to tunicamycin.
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Regulation of the Replication of Influenza Virus RNA Segments: Partial Suppression of Protein Synthesis Restores the ‘Early’ Replication Pattern
More LessSummaryThe replication of influenza virus RNA was monitored by RNA-RNA hybridization with subsequent analysis of hybrid duplexes, as well as by immunosorbtion of viral nucleocapsids from extracts of [3H]uridine-labelled cells followed by the isolation and characterization of nucleocapsid-associated RNA. The nucleocapsid-associated RNA preparations contained mostly negative-strand genomic RNA. Electrophoresis of the hybrid RNA duplexes or single-stranded nucleocapsid-associated RNA in polyacrylamide gel revealed an ‘early’ replication pattern, with a predominance of the NP and NS gene segments, in cells labelled from 0 to 1 h post-infection. At later stages of infection the pattern changed to the ‘late’ one, with the M gene segment in excess of NS, and the NP gene no longer predominant. Cycloheximide added as late as 2 or 3 h post-infection suppressed RNA replication. Moderate concentrations of cycloheximide inhibited the replication of NS and NP gene segments to a lesser degree than the replication of the other RNA segments, thus restoring the ‘early’ replication pattern. Cycloheximide treatment resulted in a slight increase in the percentage of positive strands in nucleocapsid-associated RNA. The role of protein synthesis in the transition from the ‘early’ to the ‘late’ pattern of influenza virus RNA synthesis is discussed.
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Guanidine Uptake by HeLa Cells and Its Inhibition by Some Antiguanidine Agents
More LessSummaryTo understand better the action of guanidine and its antagonists on poliovirus replication, guanidine uptake by HeLa cells was studied. It was discovered that guanidine entered HeLa cells by at least two different mechanisms. At low concentrations (< 2 mm), it was transported mostly by a carrier-mediated, saturable mechanism with an apparent affinity constant of 1·26 mm-guanidine. About a third of uptake by this mechanism was sensitive to valinomycin and possibly dependent on membrane potential difference. At higher concentrations (5 to 10 mm), transport was predominantly by a non-saturable, low affinity process. The carrier-mediated transport mechanism was similar to the organic cation H+ exchanger-mediated excretion of organic cations from the kidney, because it was inhibited by organic cations and by high [Li+]. Physiological [Na+] caused less but significant inhibition of guanidine uptake by HeLa cells. Approximately 20% of total uptake could not be inhibited with organic cations and was probably due to diffusion. The antiguanidine agents choline, dimethylethanolamine and tetraethylammonium, but not methionine, inhibited guanidine uptake by HeLa cells. The inhibition caused by these agents depended on their concentration and more or less paralleled their reported ability to block guanidine inhibition of poliovirus replication. Even though choline inhibited guanidine uptake it appeared to reverse this inhibition of virus replication primarily by blocking the intracellular action of guanidine. Some unexplained previous observations on the action of guanidine and its antagonists were discussed in view of the results of this study.
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Intracellular Reovirus Survives Cytotoxic T Lymphocyte-mediated Lysis of its Host Cell
More LessSummaryCytotoxic T lymphocytes (CTLs) induce rapid, extensive internal disintegration in target cells and this is unique among immune lytic mechanisms studied. This raises the question of whether CTLs are uniquely capable of halting virus infections by inducing damage within the target cell causing inactivation of intracellular virus. Reovirus infection of mouse P815 cells provided a suitable system for evaluating this question. An increase in cell-associated infectious virions began 8 h after infection and increased until 20 h post-infection, at which time the titre levelled off at about 100- to 1000-fold higher than the initial value. The infectious activity was compared between host cells killed by CTLs and those killed by sonication at various points in the infection cycle. The presence of reovirus within the target cell did not inhibit the usual internal disintegration events associated with the death of a target killed by CTLs. Nevertheless, the results indicated that CTLs were incapable of inactivating intracellular reovirus at any point in the life cycle of the virus: CTL-induced cytolysis simply released the infectious virions into the medium. Thus, at least in the case of reovirus, the utility of direct killing by CTLs would appear to be limited to reduction of the virus yield by lysis of the host cell before virus replication and assembly is completed.
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Activation of Endogenous Retroviral Genomes in Mov Strains of Mice
More LessSummaryA collection of Mov mouse strains, each carrying in their germ line a Moloney murine leukaemia virus (M-MuLV) proviral genome at a different chromosomal location, was used to study expression of endogenous retroviruses. No M-MuLV - specific RNA was detected in the non-viraemic Mov strains studied, indicating that less than two copies of RNA are transcribed per cell. Virus expression was seen in three viraemic Mov strains. In Mov-3 mice the provirus was activated shortly after birth, whereas proviruses in Mov-9 and Mov-14 were activated at different stages of embryogenesis. The results suggest that the chromosomal position influences proviral expression during development. The first appearance of virus particles was hot accompanied by detectable amounts of viral transcripts, suggesting that viraemia is a consequence of provirus activation in a small, as yet unidentified, population of cells, followed by virus spread and infection of susceptible cells.
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Transcriptional Activation of the Major Immediate Early Transcription Unit of Human Cytomegalovirus by Heat-shock, Arsenite and Protein Synthesis Inhibitors
SummaryIn Rat-9G cells several copies of the major immediate early (IE) transcription unit (regions 1 and 2) of the human cytomegalovirus (HCMV) are stably integrated. The cells show a repressed phenotype for IE expression but can be induced by inhibition of protein synthesis. In this report we present evidence that the repressed phenotype is due to the absence of IE transcription and that heat-shock and sodium arsenite treatments each result in the transcriptional activation of the repressed IE transcription unit. Either treatment resulted in the induction of HCMV IE transcripts and IE nuclear antigen expression. An octameric DNA sequence present in three of the 18 bp IE enhancer elements (GGACTTTC) resembles the cellular heat-shock element core consensus sequence and may therefore be involved in the heat-shock response.
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Identification of Human Papillomavirus Type 16 E7 Protein by Monoclonal Antibodies
More LessSummaryA number of human papillomavirus (HPV) type 16 proteins have recently been identified in human cervical carcinoma cell lines using polyclonal antisera against papillomavirus gene products expressed in Escherichia coli. E7 protein has been found to be the most abundant papillomavirus protein in these cells. Here we describe a panel of monoclonal antibodies recognizing a 15K non-glycosylated cytoplasmic HPV-16 E7 protein. One of the antibodies cross-reacted with HPV-18 E7 protein.
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Single Amino Acid Substitution of Sendai Virus at the Cleavage Site of the Fusion Protein Confers Trypsin Resistance
More LessSummaryAmino acid sequences of fusion (F) proteins of two trypsin-resistant mutants of Sendai virus, TR-2 and TR-5, were deduced from nucleotide analysis of cDNA encoding the F gene and were compared with that of the trypsin-sensitive wild-type Sendai virus. In both mutants, amino acid substitutions were found at residues 116 (Arg → He), the cleavage site of the F protein, and 109 (Asn → Asp). Two trypsin- sensitive revertants, TSrev-52 and TSrev-58, derived from TR-5 were both activated by trypsin similarly to the wild-type virus and had a single amino acid reversion from lie to Arg at residue 116, leaving Asp as before at residue 109. These results indicate that the trypsin sensitivity of Sendai virus can be changed by a single amino acid substitution at the cleavage site of the F protein and a mutation from Arg to lie is responsible for the acquisition of resistance to trypsin.
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Selection and Characterization of Interferon-sensitive Cells Derived from an Interferon-resistant NIH 3T3 Line
More LessSummaryWe have developed a selection protocol to isolate interferon (IFN)-sensitive subclones directly from an IFN-resistant cell population. The protocol uses encephalo- myocarditis virus (EMCV) as a selection agent in combination with pretreatment with low doses of IFN and subsequent growth in the presence of virus-neutralizing antiserum. We have applied this protocol to the partially IFN-resistant NIH 3T3 clone 1 line and have obtained a number of IFN-sensitive subclones. Sensitivity to IFN was restricted to protection against EMCV. Replication of vesicular stomatitis virus as well as cell growth were resistant to IFN treatment as in the original clone 1 line. We have compared levels of 2′,5′-oligoadenylate (2–5A) synthetase, dsRNA-activated protein kinase and 2–5A-dependent RNase in some IFN-sensitive subclones and found no difference from the resistant clone 1 cells. Markedly decreased levels of 2–5A- dependent RNase and thus a defective 2–5A pathway have been implicated as a possible cause for the partial resistance of clone 1 cells to IFN. Since the selected IFN- sensitive subclones are of the same phenotype in this respect as the clone 1 line we suggest that inhibition of EMCV in these lines occurs through a mechanism independent of the 2–5A system.
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Characterization of Proteins Associated with Hepatitis Delta Virus
More LessSummaryThe number and size of proteins associated with hepatitis delta virus (HDV) from serum and liver (human, chimpanzee and woodchuck) in the acute and chronic stages of HDV infection were analysed by immunoblotting. HDV particles in serum were separated from serum proteins by gel filtration and peak fractions of HDV antigens were subjected to PAGE. Immunoblotting with human anti-HDV-positive sera and 125I-labelled Protein A revealed two bands of 27K and 29K. It was not possible to identify any core-like structure from liver homogenates by CsCl gradient centrifugation. HDV proteins from such gradients were degraded to a size of 14K as determined by immunoblotting. HDV RNA was found in fractions at a density of 1·5 g/ml. However, direct homogenization of liver tissue in gel electrophoresis sample buffer, followed by PAGE and immunoblotting resulted in identification of HDV-associated proteins of 27K and 29K, indicating that HDV proteins in liver tissue are the same size as those in serum, but that they degrade rapidly. There was no difference in size of HDV proteins in liver samples from humans, chimpanzees or woodchucks.
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Biophysical Characterization of Rotavirus Particles Containing Rearranged Genomes
More LessSummaryHuman rotaviruses containing rearranged genomes were found to package up to 1800 additional base pairs in virus particles. The viruses compared were indistinguishable in respect of their particle diameters and their apparent S values. Particles containing rearranged genomes were found to be of a higher density than rotavirus particles containing a standard genome as determined by equilibrium density ultracentrifugation. The increase in density was directly proportional to the number of additionally packaged base pairs.
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Variation in the Bluetongue Virus Neutralization Protein VP2
More LessSummaryTo determine the extent and nature of the antigenic variation of four U.S.A. serotypes of bluetongue virus (BTV), the complete nucleotide sequence was determined for cDNA clones representing the L2 dsRNA of BTV serotype 13, the gene that codes for the outer capsid neutralization antigen (VP2). The predicted amino acid sequence of the protein was compared with the VP2 sequences of the U.S.A. serotypes of BTV-10, BTV-11 and BTV-17. Diagon comparisons, hydropathic plots and analyses of potential secondary structure of the four proteins indicated that all four VP2 proteins were structurally similar. However, the VP2 protein of BTV-13 was found to exhibit only 40% homology with the VP2 species of the other three viruses. The comparative sequence data indicated that there were regions of the proteins with greater variability than other regions, as expected for proteins that vary antigenically but are structurally similar.
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Expression of Bovine Rotavirus Neutralization Antigen in Escherichia coli
SummaryA 646 bp fragment derived from a full length cDNA clone of genomic segment 9 of bovine rotavirus (NCDV strain) was inserted into Escherichia coli expression plasmid pEXl. The fragment encodes amino acids 50 to 265 of the major vital neutralization antigen VP7, a 326 amino acid long outer shell glycoprotein. Several transformed bacterial clones were isolated in which the recombinant plasmid directed the synthesis of a cro-β-galactosidase -VP7 fusion protein that was recognized by rabbit polyclonal antibodies against NCDV rotavirus. Sera from rabbits immunized with the fusion protein specifically reacted with VP7 among NCDV virion polypeptides. The chimeric polypeptide was also specifically recognized by two monoclonal antibodies against UK strain rotavirus VP7 that exhibited virus-neutralizing activity. However, immune sera to the chimeric polypeptide showed no neutralizing activity against bovine rotavirus. These results are discussed in view of a recent report that a fusion VP7-β-galactosidase polypeptide comprising 35 more amino acids at the carboxy terminus was able to induce neutralizing antibodies in mice to simian rotavirus SA11
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- Plant
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Interference between Cowpea Mosaic Virus and Cowpea Severe Mosaic Virus in a Cowpea Host Immune to Cowpea Mosaic Virus
More LessSummaryInfection of a cowpea line by cowpea severe mosaic virus (CPSMV) was inhibited by cowpea mosaic virus (CPMV) even though the plants were immune to CPMV. The inhibition was dose-dependent and was complete if CPMV was added to the inoculum in a 50-fold excess over CPSMV. Isolated CPMV RNA inhibited infection by CPSMV or by isolated CPSMV RNA. CPMV particles devoid of RNA (top component), u.v.-inactivated but intact CPMV particles or u.v.-inactivated CPMV RNA did not inhibit infection by CPSMV. Bottom component particles of CPMV, but not middle component particles, inhibited CPSMV to the same extent as unfractionated CPMV. These findings strongly suggest that the interference is not due to competition between the particles or the RNAs of the two viruses for infectible sites. It may be that CPMV infects cells of the ‘immune’ host subliminally and that the inhibition is associated with replication of at least bottom component RNA of CPMV.
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The Genome-linked Protein of Cherry Leaf Roll Virus
More LessSummaryThe structures at the 5′ termini of the two genomic RNA species of cherry leaf roll virus (CLRV) were found to be neither 7-methylguanosine caps, nor 5′-hydroxyl groups or 5′-phosphate groups. CLRV RNA could be iodinated using Na125I and Iodogen; the labelled moiety appeared to be covalently linked to the RNA and could be removed by treatment with Pronase or proteinase K without altering the electrophoretic mobility of the RNA. The infectivity of RNA was greatly diminished by these enzymes, but such treatment impaired neither the fidelity nor the efficiency of translation of the RNA in vitro. Electrophoresis of the acetone-precipitable material released from the RNA by ribonuclease A treatment yielded a single radioactive component corresponding in mobility to a protein with a mol. wt. of about 3500. This molecule (VPg) presumably corresponds to the protease-sensitive structure needed for infectivity. An antiserum prepared against RNA of the birch isolate of CLRV precipitated homologous VPg as well as those of the rhubarb, dogwood, walnut and Sambucus racemosa isolates of CLRV, but not the VPgs of arabis mosaic nepovirus or tomato black ring nepovirus.
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- Fungal
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Identification and Comparison of Viral Genes Coding for Capsid Proteins of Ustilago maydis Virus
More LessSummaryDirect evidence linking the capsid protein to specific dsRNA segments from the three killer strains of Ustilago maydis virus (P1, P4, P6) is presented. The capsid proteins of the three strains cross-react immunologically, have similar mol. wt. and similar peptide maps after limited proteolysis. The capsid proteins from P1 and P4 were translated from their respective H2 dsRNA segments, whereas the capsid protein for P6 was translated from H1 dsRNA. These in vitro translation products were each precipitated by the antiserum to capsid proteins of all three strains, had similar mol. wt. and similar peptide maps. All in vitro translation products competed effectively with native capsid proteins of all of the three strains in immunocompetition assays. These results suggest that the three strains code for a similar capsid protein, and that the information for capsid protein resides in the H2 segment of strain P1 and P4, and in the H1 segment of strain P6.
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Volume 18 (1973)
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Volume 17 (1972)
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Volume 16 (1972)
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Volume 15 (1972)
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Volume 14 (1972)
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Volume 13 (1971)
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Volume 12 (1971)
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Volume 11 (1971)
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Volume 10 (1971)
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Volume 9 (1970)
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Volume 8 (1970)
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Volume 7 (1970)
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Volume 6 (1970)
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Volume 5 (1969)
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Volume 4 (1969)
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Volume 3 (1968)
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Volume 2 (1968)
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Volume 1 (1967)