Editorial: Mechanisms of resistance and host responses to RNA virus infections.
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functional genomics↗
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Selective blockage of initiation of host protein synthesis in RNA-virus-infected cells.
Poliovirus mRNA and mRNA transcribed from vesicular stomatitis virus and reovirus genomes efficiently direct protein synthesis in vivo under experimental conditions where the initiation of host protein synthesis is selectively blocked. The selective blockage of host peptide chain initiation after exposure to hypertonic medium indicates that the translation of viral mRNA is more efficiently initiated than is the translation of host mRNA. It further suggests that virus directed suppression of host protein synthesis could proceed by a mechanism involving a nonspecific decrease in the rate of peptide chain initiation. Exposure of infected cells to hypertonic medium provides a unique tool with which to study early events in the infectious cycle by permitting the efficient unmasking of virus-specific poly-peptide synthesis.
Animals↗
Polysomal RNA in Semliki Forest virus infected Aedes albopictus cells.
Polysomes from Aedes albopictus cells were identified by their rapid labelling with radioactive amino acids and their sensitivity to EDTA, RNase and puromycin. The major ribosome component in cytoplasmic extracts had a sedimentation coefficient of approx. 95S and may be a ribosome dimer. In Semiki Forest virus infected Aedes albopictus cells, 42S and 26S RNA were the major virus RNA species detected up to 10 h post infection. Virus RNA was detected in association with pre-labelled ribosomes and banded at a buoyant density of 1-55 g/ml. 42S, 38S and 26S virus RNA species were associated with polysomes.
Aedes↗
Absence of poly (A) from the infective RNA of Nodamura virus.
With the exception of phage Qbeta, the RNAs of all the other small icosahedral RNA viruses so far examined contain a poly (A) tract. This tract has been implicated in the infectivity of poliovirus RNA. We have now shown that Nodamura virus, a divided genome virus from which infective RNA can be extracted, does not contain any poly (A) tracts. This evidence with Nodamura virus shows that poly (A) is not a necessary requirement for the infectivity of virus RNA molecules.
Aphthovirus↗
Enhancement of infectivity of encephalomyocarditis virus RNA by amphotericin B methyl ester.
The methyl ester of amphotericin B (AmBME), a macrolide polyene antibiotic, enhanced the infectivity of encephalomyocarditis (EMC) virus RNA for L929 cells. AmBME alone (100 microgram/ml) resulted in increases in EMC virus RNA infectivity of 10- to 100-fold. Addition of DEAE dextran at concentrations (5 microgram/ml), which alone slightly suppressed EMC virus RNA infectivity, further augmented the effects of AmBME (augmentation in infectivity up to 750-fold). AmBME did not inhibit RNase, did not enhance EMC virus infectivity and increased infectivity of EMC virus RNA which was already cell-associated. The polyenes are probably acting by increasing intracellular penetration of polyribonucleotides.
Amphotericin B↗
[Presence of autocomplementary RNA with viral specificity in cells infected with herpes virus].
RNA from cells infected with Herpes simplex virus contain a higher percentage of double-stranded RNA than non-infected cells. This percentage increases three-fold upon self-annealing. The complementary RNA sequences were shown to be virus-specific by the following criteria: (1) high melting temperature than double-stranded RNA from non infected cells; (2) higher density in caesium sulphate; (3) specific hybridization with viral DNA.
Animals↗
Trichomonas vaginalis resistance to Mengo virus infection.
We have investigated the susceptibility of Trichomonas vaginalis to Mengo virus infection by comparing the outcome of Mengo virus or purified Mengo virus RNA infection in T. vaginalis and in CCL-1 mouse fibroblasts. While the adsorption and entry of Mengo virus into T. vaginalis occurred in the same manner as in fibroblasts, the uncoating was much slower. In addition, Mengo virus infection of T. vaginalis displayed no eclipse nor any subsequent production of infectious virus. Purified RNA failed to initiate productive infection in T. vaginalis, whereas it provoked viral replication in the fibroblast controls. It was shown by assessment of protein synthesis in T. vaginalis and mouse fibroblasts cell-free systems that the protozoan ribosomes were able to translate endogenous mRNA and poly-U, but not viral RNA.
Animals↗
NAT10 is critical to block RNA sensing-induced IFN-β transactivation in viral infection.
UNLABELLED: Cells detect invading viruses and produce type I interferons (IFNs) to stimulate an innate antiviral effector response. However, IFN levels must be fine-tuned to achieve antiviral efficacy while limiting hyperinflammatory and tissue-damaging effects. Here, we report that NAT10, a histone and cytidine acetyltransferase, regulates the production of type I IFNs and RNA virus infections. Depletion of NAT10 increased the expression of IFN-β and IFN-stimulated genes, and correspondingly impaired viral replication. Mechanistically, NAT10 dynamically associated with the IFN-β promoter and also negatively regulated IRF3's chromatin associations through modulation of long noncoding RNAs that inhibit IRF3. Treatment of cells with Remodelin, a NAT10 inhibitor, similarly increased IFN-β expression and inhibited viral infections. Overall, our findings reveal NAT10 is a potential host-directed target for antiviral treatment via regulation of type I IFN. IMPORTANCE: Type I interferons (IFNs) signaling pathway is critical to cellular defense and innate immunity against evading pathogens, including viruses. However, induction of type I IFNs is fine-tuned to achieve the antiviral consequence while maintaining host cellular homeostasis. This paper presents a novel mechanism for the NAT10 protein to silence IFN-β induction through modulation of IRF3 activity at the promoter of IFN-β, and further demonstrates the therapeutic potential of the NAT10 inhibitor Remodelin to restrict viral infection while inducing IFN-β.
Interferon-beta↗
Low oncogenic potential of avian endogenous RNA tumor virus infection or expression.
Of chickens either spontaneously producing or exogenously infected in ovo with Rous-associated virus, type O (RAV-O), an endogenous virus of the chicken, only 1 died with lymphoid leukosis (LL), the most common neoplasm associated with the leukosis-sarcoma virus group. Because the chickens were not kept in strict isolation, it could not be assumed that the one LL was induced by RAV-O. In contrast, RAV-1-infected chickens from the same lines had a high incidence of LL and other neoplasms. Over 800 chickens of several inbred lines were maintained in plastic isolators free of exogenous avian leukosis-sarcoma virus infection for from 500 to nearly 1,000 days of age. No LL was observed, even though some lines are known to produce RAV-O spontaneously or to express inherited gs antigen. Three neoplasms of unknown etiology were observed, but none generally associated with leukosis virus infection. We concluded that avian endogenous virus expression had little, if any, oncogenic potential, and that exogenous avian leukosis viruses were responsible for most naturally occurring neoplasms.
Animals↗
Proteins bound to heterogeneous nuclear RNA of simian-virus-40-infected cells.
Heterogeneous nuclear RNA . protein (hnRNA . protein) complexes from simian-virus-40 (SV40)-infected cells late in infection contain 7--10% RNA sequences specific to SV40 DNA. The SV40 nuclear RNA . protein complexes sediment at 60--70 S. The reality and specificity of the RNA-protein association is shown in metrizamide gradients. Protein and RNA lebels of hnRNA . protein-particles in SV40-infected cells follow a parallel pattern with a peak at 1.28 g/cm2 whereas a mixture of ribosomal RNA and soluble cytoplasmic proteins is separated according to the different densities in metrizamide. Analysis of hnRNA . protein from infected cells by two-dimensional gel electrophoresis shows the presence of a number of new proteins. It is demonstrated that three of these proteins are cellular ones induced by the virus infection and hence constitute good candidates to be specific RNA . protein particles for virus nuclear RNA. The presence of actin in hnRNA . protein particles from normal and SV40-infected cells and the presence of the major capsid protein VP1 in hnRNA . protein particles from SV40-infected cells is discussed.
Base Sequence↗
A newly established reverse genetic system for a circular RNA virus reveals new requirements for infection and its biocontrol potential.
Ambiviruses are fungal-infecting circular RNA viruses that uniquely combine viroid-like and viral features, yet the function of their conserved ORF-B protein and their effects on hosts remain unknown, hindered by the lack of a reverse genetics system. Here, we constructed the first infectious cDNA clone of an ambivirus, Fusarium graminearum ambivirus 1 (FgAV1), using a head-to-tail dimer placed downstream of a fungal promoter. FgAV1 was horizontally transmitted via hyphal anastomosis to virus-free Fusarium graminearum strains. Notably, a reverse-oriented dimer construct was also infectious and transmissible. Targeted mutagenesis revealed that both ORF-A- and ORF-B-encoded proteins and the presence of embedded ribozymes are indispensable for ambivirus replication. Our results further demonstrate that FgAV1 infection triggers a fungal RNAi response, extending the antiviral role of host sRNAs to circular RNA viruses. Furthermore, FgAV1 infection suppressed fungal growth and significantly reduced the virulence of F. graminearum on wheat. These findings provide novel insights into ambivirus replication and their potential in fungal pathogen biocontrol.
RNA Viruses↗
Requirement of an adenylic acid-rich segment for the infectivity of encephalomyocarditis virus RNA.
About 80% of the RNA molecules extracted from encephalomyocarditis (EMC) virus were bound by oligo(dT)-cellulose under conditions which bind poly(A) but not poly(C) nor ribosomal RNA. This shows that most EMC virus RNA molecules contain a poly(A) tract. Both bound and unbound fractions contained RNA molecules of apparently the same size when examined by sucrose gradient sedimentation, but the bound fraction contained an adenylic acid-rich segment of about 20 nucleotides long, whereas the unbound RNA did not. The bound RNA had 200 times the specific infectivity of the unbound RNA which suggests that the poly(A) tract present in EMC virus RNA is required for infectivity.
Adenosine Monophosphate↗
Natural self-attenuation of pathogenic viruses by deleting the silencing suppressor coding sequence for long-term plant-virus coexistence.
Potyviridae is the largest family of plant-infecting RNA viruses. All members of the family (potyvirids) have single-stranded positive-sense RNA genomes, with polyprotein processing as the expression strategy. The 5'-proximal regions of all potyvirids, except bymoviruses, encode two types of leader proteases: the serine protease P1 and the cysteine protease HCPro. However, their arrangement and sequence composition vary greatly among genera or even species. The leader proteases play multiple important roles in different potyvirid-host combinations, including RNA silencing suppression and virus transmission. Here, we report that viruses in the genus Arepavirus, which encode two HCPro leader proteases in tandem (HCPro1-HCPro2), can naturally lose the coding sequences for these two proteins during infection. Notably, this loss is associated with a shift in foliage symptoms from severe necrosis to mild chlorosis or even asymptomatic infections. Further analysis revealed that the deleted region is flanked by two short repeated sequences in the parental isolates, suggesting that recombination during virus replication likely drives this genomic deletion. Reverse genetic approaches confirmed that the loss of leader proteases weakens RNA silencing suppression and other critical functions. A field survey of areca palm trees displaying varied symptom severity identified a transitional stage in which full-length viruses and deletion mutants coexist in the same tree. Based on these findings, we propose a scenario in which full-length isolates drive robust infections and facilitate plant-to-plant transmission, eventually giving rise to leader protease-less variants that mitigate excessive damage to host trees, allowing long-term coexistence with the perennial host. To our knowledge, this is the first report of potyvirid self-attenuation via coding sequence loss.
Plant Diseases↗
[Infectivity of fowl plague virus RNA in the process of infection].
The conditions for isolation and detection of the infectious properties of nucleic acid preparations extracted from cells infected with fowl plague virus were studied. It is suggested that double-stranded virus-specific RNAs possess the infectious properties.
Cells, Cultured↗
Dengue Virus Replicative-Form dsRNA Is Recognized by Both RIG-I and MDA5 to Activate Innate Immunity.
RIG-I like receptors (RLRs) are a family of cytosolic RNA sensors that sense RNA virus infection to activate innate immune response. It is generally believed that different RNA viruses are recognized by either RIG-I or MDA5, two important RLR members, depending on the nature of pathogen-associated molecular patterns (PAMPs) that are generated by RNA virus replication. Dengue virus (DENV) is an important RNA virus causing serious human diseases. Despite extensive investigations, the molecular basis of the DENV PAMP recognized by the host RLR has been poorly defined. Here, we demonstrated that the DENV infection-induced interferon response is dependent upon both RIG-I and MDA5, with RIG-I playing a predominant role. Next we purified the DENV PAMP RNA from the DENV-infected cells, and demonstrated that the purified DENV PAMP is viral full-length double-stranded RNA bearing 5'ppp modifications, likely representing the viral replicative-form RNA. Finally, we confirmed the nature of the DENV PAMP by reconstituting the viral replicative-form RNA from in vitro synthesized DENV genomic RNA. In conclusion, our work not only defined the molecular basis of the RLR-PAMP interaction during DENV infection, but also revealed the previously underappreciated recognition of a distinct moiety of the same PAMP by different RLRs in innate immunity against RNA viruses.
Interferon-Induced Helicase, IFIH1↗
Physicochemical characterization of a small RNA virus associated with baculovirus infection in Trichoplusia ni.
An RNA virus was isolated from Trichoplusia ni larvae infected with inoculum of the baculovirus of Autographa californica. Physicochemical characterization has revealed a 35-nm virus with a density in CsCl of 1.3 g/cm3 and a sedimentation coefficient of 200S. The virus consisted of 10--15% single-stranded RNA with an apparent molecular weight of 1.9 x 10(6) and coat protein with a subunit size of 67,000. The virus is similar to the Nudaurelia capensis beta virus and also possesses some interesting similarities to the mammalian caliciviruses. The proposed cryptogram of the virus is R/1:1.9/12:S/S:I/O.
Animals↗
Ramu stunt virus genome reveals previously unreported segments and nucleocapsid domain duplication in Mechlorovirus.
Ramu stunt virus (RmSV), a member of the genus Mechlorovirus within the family Phenuiviridae, was previously described as a six-segmented RNA virus infecting sugarcane. In this study, we re-examined type material and additional isolates using high-throughput sequencing and RT-PCR validation, revealing that RmSV possesses a nine-segmented genome, making it the largest reported in the Phenuiviridae. This expanded architecture includes duplicated RNA segments (RNA 2a and RNA 2b) encoding nucleocapsid-like proteins and two novel segments (RNA 7 and RNA 8). Comparative analysis showed that RNA 2a and 2b share about 84% amino acid identity, while RNA 5 encodes a third nucleocapsid homolog, indicating unprecedented domain redundancy. Structural modeling confirmed that all three nucleocapsid proteins maintain a conserved fold despite low sequence identity, with electrostatic mapping suggesting differential RNA-binding potential. Additionally, RNA 6 encodes a hypothetical protein structurally similar to the rice stripe virus disease-specific S-protein, implicating a role in symptom development. Transcript abundance analysis revealed RNA 6 as the most highly expressed segment across isolates. These findings revise the genomic composition of RmSV, highlight mechanisms of genome plasticity and adaptive evolution in plant-infecting bunyaviruses, and underscore practical implications for diagnostic assay design, resistance breeding, and biosecurity surveillance.
Genome, Viral↗
A rapid method for the quantitative study of RNA from canine distemper virus infected cells.
Centrifugation through CsCl was used to isolate 32P-labelled RNA in a one-step purification procedure. The method is suitable for quantitative as well as preparative studies and appears to have considerable advantages over conventional methods of RNA extraction. We have used this procedure to investigate the RNA synthesized in Vero cells infected with canine distemper virus (CDV). We show that the combination of CsCl centrifugation and affinity chromatography on poly-U Sepharose provides a rapid method for isolating messenger RNA from virus infected cells.
Cell Line↗