Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.6 (RNA polymerase)
34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have demonstrated by recombination of two highly pathogenic avian influenza viruses [A/FPV/Rostock (Hav1N1) x A/turkey/England/63 (Hav1Nav3)] that recombinants can be isolated which are pathogenic as well as non-pathogenic for chickens. They carried the glycoproteins of either parent strains, and all are produced in infectious form in chick embryo cells. Genetic analysis revealed that the non-pathogenic recombinants possess a mixed RNA polymerase complex, consisting of pol 1, pol 2, ptra and NP gene products, while, with one exception, the pathogenic recombinants have the genes coding for the polymerase activity from one or other parent virus. The biological properties of the recombinant viruses did not correlate with their pathogenicity for chickens.
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PMID:Correlation of pathogenicity and gene constellation of influenza A viruses. III. Non-pathogenic recombinants derived from highly pathogenic parent strains. 52 99

The influenza virus A/duck/Alberta/48/76 with the antigen formula H7N3 (16) and Hav1 Nav2 (WHO nomenclature from 1971) (15), respectively, as well as a nonpathogenic virus of the subtype Hav1 were purified to a high degree by ultracentrifugation in continuous sucrose gradients (15-40% w/w and 20-60% w/w, respectively). The activity of the RNA polymerase of this virus preparation was determined by incorporating 3H-UMP in acid insoluble material following preincubation of the virus with the nonionic detergens Nonidet P-40 for 15 min at 32 degrees C. The influence of different concentrations was investigated of dinucleotid, NaCl, MgCl2, Nonidet P-40 and different incubation temperatures. Optimal incorporation rates were found at following conditions: 0.2 mM dinucleotid ApG, 150 mM sodium chloride and 8 mM magnesium chloride by concentration of ions, 0.25-0.5% detergens Nonidet P-40 as well as a temperature of incubation of 32 degrees C. The data for optimal polymerase activity for the avian influenza virus A/duck/Alberta/48/76 are generally not different from the conditions described for the Fowl-Plague-Virus and for human strains.
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PMID:[Characterization of RNA polymerase activity of highly purified preparations of influenza virus A/duck/Alberta/48/76]. 637 62

Incomplete avian influenza (fowl plague) virus derived by undiluted egg passage, displayed an increased capacity to promote the synthesis of intracellular virus-specific proteins when compared with standard virus. The in vitro virion-bound RNA polymerase activity of incomplete virus was also greater than could be explained by the presence of residual infectious virus. When the titres of infectious and interfering virus species were determined directly, they did not account for all the virus present. The existence of defective non-interfering (DNI) virus, even in standard virus preparations, was inferred. DNI virus is capable of initiating infection, synthesis of mRNA and proteins but cannot complete a productive replication cycle, and does not interfere with multiplication of standard virus. Such DNI virus could exaggerate the true extent of DI virus formation by lowering the PFU:HAU ratio and so account for the failure to correlate infectivity with RNA composition or RNA polymerase activity.
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PMID:Incomplete avian influenza virus contains a defective non-interfering component. 706 1

Reverse transcriptase (RT) PCR assays have been developed to improve the diagnosis of avian influenza A. RT-PCR using primers complementary to a conserved region of the matrix protein was assessed as being suitable for the detection of influenza A virus RNA from poultry as well as from pigs, horses and humans, regardless of the haemagglutinin (HA) and neuraminidase (NA) subtype. Therefore, this RT-PCR is a valuable tool to confirm the initial diagnosis of any influenza A infection. As a second approach, experiments were performed to identify the HA gene encoding the post-translational cleavage site of potentially highly pathogenic AIV isolates by RT-PCR. The principal aim was to design one universal primer pair for each virus subtype, H5 and H7, respectively, which allows the detection of all strain variants using only one consistent method. To realize this objective, it was necessary to develop 'wobble' primers. AIV RNAs from seven H5 and 11 H7 subtype viruses included in the investigations were specifically recognized by RT-PCR using these primers. This method therefore provides a rapid, subtype-specific diagnosis and subsequent sequencing of H5 and H7 avian influenza viruses.
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PMID:Type- and subtype-specific RT-PCR assays for avian influenza A viruses (AIV). 1086 Nov 98

Highly virulent avian influenza viruses can arise from avirulent strains maintained in poultry, but evidence to support their generation from viruses in wild birds is lacking. The most likely mechanism for the acquisition of virulence by benign avian viruses is the introduction of mutations by error-prone RNA polymerase, followed by the selection of virulent viruses. To investigate whether this mechanism could apply to wild waterfowl, we studied an avirulent wild-swan virus that replicates poorly in chickens. After 24 consecutive passages by air sac inoculation, followed by five passages in chicken brain, the avirulent virus became highly pathogenic in chickens, producing a 100% mortality rate. Sequence analysis at the hemmaglutinin cleavage site of the original isolate revealed a typical avirulence type of sequence, R-E-T-R, which progressed incrementally to a typical virulence type of sequence, R-R-K-K-R, during repeated passages in chickens. These results demonstrate that avirulent viruses maintained in wild waterfowl in nature and bearing the consensus avirulence type sequence R-E-T-R have the potential to become highly pathogenic while circulating in chickens.
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PMID:Generation of a highly pathogenic avian influenza A virus from an avirulent field isolate by passaging in chickens. 1128 97

Eight-plasmid system was used for the generation of Avian influenza virus (AIV) strain A/Chicken/Shanghai/F/98 (H9N2) which was isolated in China in 1998. In this plasmid-based expression system, viral cDNA was inserted beteen the RNA polymerase I (pol I) promoter and terminator sequences. The entire pol I transcription unit was flanked by an RNA polymerase II (pol II) promoter and a poly (A) site. Twenty-four hours after the transfection of eight expression plasmid into cos1 cells, the supernatant and cos1 cells transfected were inoculated into the allantoic cavity of 10-day-old specific-pothgen-free (SPF) chicken eggs. The HA titer was determined after passage of the rescued virus in chicken eggs, and as high as that of the parental wild-type virus.
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PMID:[Generation of A/Chicken/Shanghai/F/98 (H9N2) avian influenza virus from eight plasmids]. 1598 29

Influenza virus RNA polymerase is a heterotrimeric complex consisting of PB1, PB2, and PA subunits. These polymerase subunits accumulate in the nucleus of infected cells. We report here that PB2, from both human and avian influenza viruses, could also localize to mitochondria in transfected cells. Importantly, cells infected with influenza A virus also displayed mitochondrial PB2. We show that an N-terminal motif composed of 120 amino acids is sufficient for localization of PB2 to mitochondria. In particular, leucine residues at positions 7 and 10 were essential for mitochondrial targeting. Recombinant influenza A/WSN/33 viruses expressing PB2 proteins with L7A and/or L10A mutations showed reduced viral titers, but unaffected levels of transcription, replication, and protein expression. The introduction of L7A and/or L10A mutations into recombinant viruses correlated with reduced mitochondrial membrane potential in infected cells, suggesting that mitochondrial localization of PB2 contributes to the preservation of mitochondrial function during influenza virus infection.
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PMID:Characterization of a mitochondrial-targeting signal in the PB2 protein of influenza viruses. 1624 67

The generation of vaccines for highly pathogenic avian influenza viruses, including those of the H5N1 subtype, relies on reverse genetics, which allows the production of influenza viruses from cloned cDNA. In the future, reverse genetics will likely be the method of choice for the generation of conventional influenza vaccine strains because gene reassortment by more traditional methods is cumbersome. Established systems for the artificial generation of influenza A viruses require transfection of cells with the eight to 12 plasmids that provide the eight influenza viral RNAs as well as the polymerase and nucleoproteins of the virus. However, cell lines appropriate for human vaccine production (e.g., Vero cells) cannot be transfected with high efficiencies. To overcome these problems, we established a reverse genetics system in which the eight RNA polymerase I transcription cassettes for viral RNA synthesis are combined on one plasmid. Similarly, two cassettes encoding the hemagglutinin and neuraminidase segments and six cassettes encoding the remaining proteins were combined. We also combined three RNA polymerase II transcription cassettes for the expression of the polymerase subunits. By combining these cassettes, we reduced the number of plasmids required for virus generation significantly and produced influenza A virus in Vero cells with higher efficiency than with the traditional 12 plasmid system. This new system is thus suitable for influenza virus vaccine production and may be applicable to other reverse genetics systems that rely on the introduction of several plasmids into eukaryotic cells.
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PMID:An improved reverse genetics system for influenza A virus generation and its implications for vaccine production. 1626 34

Influenza A viruses cause pandemics at random intervals. Pandemics are caused by viruses that contain a hemagglutinin (HA) surface glycoprotein to which human populations are immunologically naive. Such an HA can be introduced into the human population through reassortment between human and avian virus strains or through the direct transfer of an avian influenza virus to humans. The factors that determine the interspecies transmission and pathogenicity of influenza viruses are still poorly understood; however, the HA protein plays an important role in overcoming the interspecies barrier and in virulence in avian influenza viruses. Recently, the RNA polymerase (PB2) protein has also been recognized as a critical factor in host range restriction, while the nonstructural (NS1) protein affects the initial host immune responses. We summarize current knowledge of viral factors that determine host range restriction and pathogenicity of influenza A viruses.
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PMID:Host range restriction and pathogenicity in the context of influenza pandemic. 1670 41

This case report describes the course of an outbreak of avian influenza on a Dutch turkey farm. When clinical signs were observed their cause remained unclear. However, serum samples taken for the monitoring campaign launched during the epidemic of highly pathogenic avian influenza in 2003, showed that all the remaining turkeys were seropositive against an H7 strain of avian influenza virus, and the virus was subsequently isolated from stored carcases. The results of a reverse-transcriptase pcr showed that a H7N3 strain was involved, and it was characterised as of low pathogenicity. However, its intravenous pathogenicity index was 2.4, characterising it as of high pathogenicity, suggesting that a mixture of strains of low and high pathogenicity may have been present in the isolate. The outbreak remained limited to three farms.
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PMID:Outbreak of avian influenza H7N3 on a turkey farm in the Netherlands. 1699 95


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