The RNA genome of Seneca Valley virus (SVV), a recently identified picornavirus, contains an internal ribosome entry site (IRES) element which has structural and functional similarity to that from classical swine fever virus (CSFV) and hepatitis C virus, members of the Flaviviridae. The SVV IRES has an absolute requirement for the presence of a short region of virus-coding sequence to allow it to function either in cells or in rabbit reticulocyte lysate. The IRES activity does not require the translation initiation factor eIF4A or intact eIF4G. The predicted secondary structure indicates that the SVV IRES is more closely related to the CSFV IRES, including the presence of a bipartite IIId domain. Mutagenesis of the SVV IRES, coupled to functional assays, support the core elements of the IRES structure model, but surprisingly, deletion of the conserved IIId 2 domain had no effect on IRES activity, including 40S and eIF3 binding. This is the first example of a picornavirus IRES that is most closely related to the CSFV IRES and suggests the possibility of multiple, independent recombination events between the genomes of the Picornaviridae and Flaviviridae to give rise to similar IRES elements.Seneca Valley virus (SVV) is a recently discovered member of the picornavirus family. It was found as a contaminant in PER.C6 cell cultures, and its natural host has not yet been definitively identified, but a number of closely related viruses have been isolated from pigs (16). The complete genome sequence of SVV-001 (16) and the crystal structure of the virus capsid (52) have now been determined. The virus is most closely related to the cardioviruses, but there are some significant differences (see below), and hence it has been recommended that the virus is classified as a new species within a new genus (Senecavirus) of the Picornaviridae.SVV-001 and two of the related viruses (isolates 1278 and 66289) were inoculated into pigs; evidence of viral replication was obtained for all three viruses and for transmission of isolate 66289. However, in none of the experiments was any sign of illness observed (unpublished data and personal communication from J. Landgraf, USDA). An important feature of SVV is its ability to replicate selectively within human tumor cells. Owing to this novel activity and lack of observed pathogenicity in animals and humans, there is interest in using SVV as an oncolytic virus against neuroendocrine cancers (39), for which it is currently in clinical trials.All picornaviruses have a positive-sense, single-stranded RNA genome that is infectious and has to act both as an mRNA and as a template for RNA replication (32). Picornavirus RNA includes a single large open reading frame (ORF), encoding a polyprotein, which is flanked by a long 5Ј untranslated region (UTR) of approximately 600 to 1,300 nucleotides (nt) (depending on the virus) plus a shorter 3Ј UTR (Ͻ100 nt) with a poly(A) tail. The viral RNA lacks the 5Ј m 7 GpppN... cap structure found on all eukaryotic cytoplasmic mRNAs. Instead, a small virus-enco...
Avian encephalomyelitis virus (AEV) is a picornavirus that causes disease in poultry worldwide, and flocks must be vaccinated for protection. AEV is currently classified within the hepatovirus genus, since its proteins are most closely related to those of hepatitis A virus (HAV). We now provide evidence that the 494-nucleotidelong 5 untranslated region of the AEV genome contains an internal ribosome entry site (IRES) element that functions efficiently in vitro and in mammalian cells. Unlike the HAV IRES, the AEV IRES is relatively short and functions in the presence of cleaved eIF4G and it is also resistant to an inhibitor of eIF4A. These properties are reminiscent of the recently discovered class of IRES elements within certain other picornaviruses, such as porcine teschovirus 1 (PTV-1). Like the PTV-1 IRES, the AEV IRES shows significant similarity to the hepatitis C virus (HCV) IRES in sequence, function, and predicted secondary structure. Furthermore, mutational analysis of the predicted pseudoknot structure at the 3 end of the AEV IRES lends support to the secondary structure we present. AEV is therefore another example of a picornavirus harboring an HCV-like IRES element within its genome, and thus, its classification within the hepatovirus genus may need to be reassessed in light of these findings.Translation initiation on the majority of cellular mRNAs is mediated by a cap-dependent mechanism. The cap structure (m 7 GpppN) found on all cytoplasmic mRNAs is recognized by the translation initiation factor complex eIF4F (reviewed in reference 28). This complex contains three proteins: eIF4E, which is the cap-binding protein; eIF4A, which has RNA helicase activity; and eIF4G, which acts as a protein scaffold between the mRNA and the 40S ribosomal subunit via its interaction with eIF3 (reviewed in reference 14). In contrast, initiation of protein synthesis on some viral mRNAs, for example, from the picornaviruses, occurs by a cap-independent mechanism termed internal initiation. In this case, translation initiation is directed by an internal ribosome entry site (IRES) element located within the 5Ј untranslated region (5ЈUTR) of the viral genome (reviewed in references 2 and 11). These IRES elements are large, typically 450 nucleotides (nt) in length, and contain extensive secondary structure; they have been shown to interact with a variety of cellular proteins (2). Most of these elements work without any requirement for eIF4E and hence can continue to function when cap-dependent protein synthesis is inhibited.The picornavirus IRES elements are divided into several groups which display distinct secondary structures and biological properties. One group (class I) contains IRES elements from the entero-and rhinoviruses (e.g., poliovirus [PV]), while the second group contains the cardio-and aphthovirus IRES elements (e.g., encephalomyocarditis virus [EMCV]). The cardio-/aphthovirus IRES elements function efficiently in the rabbit reticulocyte lysate (RRL) translation system. However, the PV and rhinovirus IRES ele...
Background: Efficient isolation and detection of low pathogenic avian influenza viruses from surveillance samples continues to be a high priority. Currently, the new cell lines are considered for supporting the replication to high virus strains titers. Objectives: The replication efficiency of a low pathogenic avian influenza virus in different origin cells was evaluated under different conditions. Materials and Methods: Chicken embryo fibroblast (CEF) cell and human alveolar epithelial cell line (A549) were infected with H9N2 at a multiplicity of infection of 0.1. The amount of infectious virus released into the cell culture supernatants at various post-infection time intervals were tittered by tissue culture infectious dose (TCID50) assay. The impact of these cells adaptation was investigated by determination the virus genes nucleotide sequences. Results: The influenza virus infectivity was not significant difference in these cells in the presence of trypsin. The results of fusion assay and determination of cellular protease confirmed that A549 cells support virus entry with or without supplemental trypsin. However, the H9N2 virus showed lower titer and infectivity in the trypsin-free infected A549 cells within longer time. The comparative sequence analysis indicated several simultaneously nucleotide substitutions were occurred in NA of the virus replicated in A549 cells resulted in two fixed amino acid changes at positions G320 to A and G414 to A up to the fifth passage. Conclusions: After seven consecutive passages of both cell cultures, the H9N2 virus showed similar antigenicity, also no change on viral titer level and virus replication behavior in adaptation was found. The results highlighted the use of A549 cells for efficient virus isolation.
Bovine viral diarrhea virus (BVDV) and bovine herpes virus-1 (BHV-1) remain as the major pathogens with heavy economic consequences in Iran. The prevalence of antibodies against BVDV and BHV-1, the rate of BVDV persistently infected (PI) animals, and associated risk factors were evaluated in a cross-sectional study carried out in Zanjan Province, Northwest Iran, in December 2011. A total number of 562 cattle in 10 herds and five cities were randomly selected, and their serum samples were tested to detect antibodies to these viruses and also BVDV antigen-positive (PI) animals. The data were analyzed with Pearson's correlation coefficient, chi-square, and logistic regression test. In total, nine and eight of the selected herds were seropositive to BVDV and BHV-1, respectively. The overall seroprevalence of these infections were estimated at 28.6 and 10.7% for BVDV and BHV-1, respectively, and 0.53% of the samples were detected as persistently infected. Statistical analysis revealed that sex, age, and farming system are risk factors for both infections (P < 0.05), while breed was determined as a strong risk factor only for BVDV (P < 0.001). In addition, the present study certainly identifies that infection with BVDV is associated with infection to BHV-1 (OR = 4.52, 95% CI: 2.60-7.80; P ˂ 0.001). The results add our knowledge about the prevalence and associated risk factors of BVDV and BHV-1 in Iran and imply that the prophylactic and surveillance strategies need to be implemented to reduce the risk of spread of these viruses.
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