scholarly journals Biogenesis of the Semliki Forest Virus RNA Replication Complex

2001 ◽  
Vol 75 (8) ◽  
pp. 3873-3884 ◽  
Author(s):  
Pekka Kujala ◽  
Anne Ikäheimonen ◽  
Neda Ehsani ◽  
Helena Vihinen ◽  
Petri Auvinen ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Rna Polymerase ◽  
Semliki Forest Virus ◽  
Rna Replication ◽  
Double Labeling ◽  
Virus Rna ◽  
Infected Cells ◽  
Em Autoradiography ◽  
The Individual ◽  
Alphavirus Infection

ABSTRACT The nonstructural (ns) proteins nsP1 to -4, the components of Semliki Forest virus (SFV) RNA polymerase, were localized in infected cells by confocal microscopy using double labeling with specific antisera against the individual ns proteins. All ns proteins were associated with large cytoplasmic vacuoles (CPV), the inner surfaces of which were covered by small invaginations, or spherules, typical of alphavirus infection. All ns proteins were localized by immuno-electron microscopy (EM) to the limiting membranes of CPV and to the spherules, together with newly labeled viral RNA. Along with earlier observations by EM-autoradiography (P. M. Grimley, I. K. Berezesky, and R. M. Friedman, J. Virol. 2:326–338, 1968), these results suggest that individual spherules represent template-associated RNA polymerase complexes. Immunoprecipitation of radiolabeled ns proteins showed that each antiserum precipitated the other three ns proteins, implying that they functioned as a complex. Double labeling with organelle-specific and anti-ns-protein antisera showed that CPV were derivatives of late endosomes and lysosomes. Indeed, CPV frequently contained endocytosed bovine serum albumin-coated gold particles, introduced into the medium at different times after infection. With time, increasing numbers of spherules were also observed on the cell surfaces; they were occasionally released into the medium, probably by secretory lysosomes. We suggest that the spherules arise by primary assembly of the RNA replication complexes at the plasma membrane, guided there by nsP1, which has affinity to lipids specific for the cytoplasmic leaflet of the plasma membrane. Endosomal recycling and fusion of CPV with the plasma membrane can circulate spherules between the plasma membrane and the endosomal-lysosomal compartment.

scholarly journals Effects of Palmitoylation of Replicase Protein nsP1 on Alphavirus Infection

2000 ◽  
Vol 74 (15) ◽  
pp. 6725-6733 ◽  
Author(s):  
Tero Ahola ◽  
Pekka Kujala ◽  
Minna Tuittila ◽  
Titta Blom ◽  
Pirjo Laakkonen ◽  
...  
Keyword(s):  
Sindbis Virus ◽  
Semliki Forest Virus ◽  
Rna Replication ◽  
Cell Types ◽  
Alkaline Solutions ◽  
Nonstructural Proteins ◽  
Replication Complex ◽  
Replication Sites ◽  
Infected Cells ◽  
Alphavirus Infection

ABSTRACT The membrane-associated alphavirus RNA replication complex contains four virus-encoded subunits, the nonstructural proteins nsP1 to nsP4. Semliki Forest virus (SFV) nsP1 is hydrophobically modified by palmitoylation of cysteines 418 to 420. Here we show that Sindbis virus nsP1 is also palmitoylated on the same site (cysteine 420). When mutations preventing nsP1 palmitoylation were introduced into the genomes of these two alphaviruses, the mutant viruses remained viable and replicated to high titers, although their growth was slightly delayed. The subcellular distribution of palmitoylation-defective nsP1 was altered in the mutant: it no longer localized to filopodial extensions, and a fraction of it was soluble. The ultrastructure of the alphavirus replication sites appeared normal, and the localization of the other nonstructural proteins was unaltered in the mutants. In both wild-type- and mutant-virus-infected cells, SFV nsP3 and nsP4 could be extracted from membranes only by alkaline solutions whereas the nsP2-membrane association was looser. Thus, the membrane binding properties of the alphavirus RNA replication complex were not determined by the palmitoylation of nsP1. The nsP1 palmitoylation-defective alphaviruses produced normal plaques in several cell types, but failed to give rise to plaques in HeLa cells, although they induced normal apoptosis of these cells. The SFV mutant was apathogenic in mice: it caused blood viremia, but no infectious virus was detected in the brain.

scholarly journals Hepatitis E Virus RNA‐Dependent RNA Polymerase is Involved in RNA Replication and Infectious Particle Production

Hepatology ◽  
2021 ◽  
Author(s):  
Noémie Oechslin ◽  
Nathalie Da Silva ◽  
Dagmara Szkolnicka ◽  
François‐Xavier Cantrelle ◽  
Xavier Hanoulle ◽  
...  
Keyword(s):  
Rna Polymerase ◽  
Hepatitis E Virus ◽  
Particle Production ◽  
Rna Replication ◽  
Hepatitis E ◽  
Rna Dependent Rna Polymerase ◽  
Infectious Particle ◽  
Virus Rna

scholarly journals Involvement of Hsp90 in Assembly and Nuclear Import of Influenza Virus RNA Polymerase Subunits

2006 ◽  
Vol 81 (3) ◽  
pp. 1339-1349 ◽  
Author(s):  
Tadasuke Naito ◽  
Fumitaka Momose ◽  
Atsushi Kawaguchi ◽  
Kyosuke Nagata
Keyword(s):  
Influenza Virus ◽  
Rna Polymerase ◽  
Nuclear Transport ◽  
Intracellular Localization ◽  
Viral Rna ◽  
Polymerase Complex ◽  
Virus Rna ◽  
Binary Complexes ◽  
Infected Cells ◽  
Rna Polymerase Subunits

ABSTRACT Transcription and replication of the influenza virus RNA genome occur in the nuclei of infected cells through the viral RNA-dependent RNA polymerase consisting of PB1, PB2, and PA. We previously identified a host factor designated RAF-1 (RNA polymerase activating factor 1) that stimulates viral RNA synthesis. RAF-1 is found to be identical to Hsp90. Here, we examined the intracellular localization of Hsp90 and viral RNA polymerase subunits and their molecular interaction. Hsp90 was found to interact with PB2 and PB1, and it was relocalized to the nucleus upon viral infection. We found that the nuclear transport of Hsp90 occurs in cells expressing PB2 alone. The nuclear transport of Hsp90 was in parallel with that of the viral RNA polymerase binary complexes, either PB1 and PB2 or PB1 and PA, as well as with that of PB2 alone. Hsp90 also interacted with the binary RNA polymerase complex PB1-PB2, and it was dissociated from the PB1-PB2 complex upon its association with PA. Furthermore, Hsp90 could form a stable PB1-PB2-Hsp90 complex prior to the formation of a ternary polymerase complex by the assembly of PA in the infected cells. These results suggest that Hsp90 is involved in the assembly and nuclear transport of viral RNA polymerase subunits, possibly as a molecular chaperone for the polymerase subunits prior to the formation of a mature ternary polymerase complex.

scholarly journals Efficient Interaction between Arenavirus Nucleoprotein (NP) and RNA-Dependent RNA Polymerase (L) Is Mediated by the Virus Nucleocapsid (NP-RNA) Template

2015 ◽  
Vol 89 (10) ◽  
pp. 5734-5738 ◽  
Author(s):  
Masaharu Iwasaki ◽  
Nhi Ngo ◽  
Beatrice Cubitt ◽  
Juan C. de la Torre
Keyword(s):  
Rna Polymerase ◽  
Gene Transcription ◽  
Viral Genome ◽  
Rna Replication ◽  
Rna Dependent Rna Polymerase ◽  
Rna Sequences ◽  
L Protein ◽  
Virus Rna

In this study, we document that efficient interaction between arenavirus nucleoprotein (NP) and RNA-dependent RNA polymerase (L protein), the twotrans-acting viral factors required for both virus RNA replication and gene transcription, requires the presence of virus-specific RNA sequences located within the untranslated 5′ and 3′ termini of the viral genome.

scholarly journals Visualization of Double-Stranded RNA in Cells Supporting Hepatitis C Virus RNA Replication

2007 ◽  
Vol 82 (5) ◽  
pp. 2182-2195 ◽  
Author(s):  
Paul Targett-Adams ◽  
Steeve Boulant ◽  
John McLauchlan
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Rna Virus ◽  
Three Dimensional ◽  
Rna Replication ◽  
Hcv Rna ◽  
Double Stranded Rna ◽  
Core Proteins ◽  
Virus Rna ◽  
Infected Cells

ABSTRACT The mechanisms involved in hepatitis C virus (HCV) RNA replication are unknown, and this aspect of the virus life cycle is not understood. It is thought that virus-encoded nonstructural proteins and RNA genomes interact on rearranged endoplasmic reticulum (ER) membranes to form replication complexes, which are believed to be sites of RNA synthesis. We report that, through the use of an antibody specific for double-stranded RNA (dsRNA), dsRNA is readily detectable in Huh-7 cells that contain replicating HCV JFH-1 genomes but is absent in control cells. Therefore, as that of other RNA virus genomes, the replication of the HCV genome may involve the generation of a dsRNA replicative intermediate. In Huh-7 cells supporting HCV RNA replication, dsRNA was observed as discrete foci, associated with virus-encoded NS5A and core proteins and identical in morphology and distribution to structures containing HCV RNA visualized by fluorescence-based hybridization methods. Three-dimensional reconstruction of deconvolved z-stack images of virus-infected cells provided detailed insight into the relationship among dsRNA foci, NS5A, the ER, and lipid droplets (LDs). This analysis revealed that dsRNA foci were located on the surface of the ER and often surrounded, partially or wholly, by a network of ER-bound NS5A protein. Additionally, virus-induced dsRNA foci were juxtaposed to LDs, attached to the ER. Thus, we report the visualization of HCV-induced dsRNA foci, the likely sites of virus RNA replication, and propose that HCV genome synthesis occurs at LD-associated sites attached to the ER in virus-infected cells.

scholarly journals Properly Folded Nonstructural Polyprotein Directs the Semliki Forest Virus Replication Complex to the Endosomal Compartment

2003 ◽  
Vol 77 (3) ◽  
pp. 1691-1702 ◽  
Author(s):  
Anne Salonen ◽  
Lidia Vasiljeva ◽  
Andres Merits ◽  
Julia Magden ◽  
Eija Jokitalo ◽  
...  
Keyword(s):  
Rna Synthesis ◽  
Semliki Forest Virus ◽  
Nonstructural Proteins ◽  
Precursor State ◽  
Replication Complex ◽  
Cytoplasmic Vesicles ◽  
Infected Cells ◽  
Membrane Bound ◽  
Intracellular Vesicles ◽  
The Individual

ABSTRACT The late RNA synthesis in alphavirus-infected cells, generating plus-strand RNAs, takes place on cytoplasmic vacuoles (CPVs), which are modified endosomes and lysosomes. The cytosolic surface of CPVs consists of regular membrane invaginations or spherules, which are the sites of RNA synthesis (P. Kujala, A. Ikäheimonen, N. Ehsani, H. Vihinen, P. Auvinen, and L. Kääriäinen J. Virol. 75:3873-3884, 2001). To understand how CPVs arise, we have expressed the individual Semliki Forest virus (SFV) nonstructural proteins nsP1 to nsP4 in different combinations, as well as their precursor polyprotein P1234 and its cleavage intermediates. A complex of nsPs was obtained from P123 or P1234, indicating that the precursor stage is essential for the assembly of the polymerase complex. To prevent the processing of the polyprotein and its cleavage intermediates, constructs with the mutation C478A (designated with a superscript CA) in the active site of the protease domain of nsP2 were used. Uncleaved polyproteins containing nsP1 were membrane bound and palmitoylated, and those containing nsP3 were phosphorylated, reflecting properties of authentic nsP1 and nsP3, respectively. Similarly, polyproteins containing nsP1 or nsP2 had enzymatic activities specific for the individual proteins, indicating that they were correctly folded in the precursor state. Uncleaved P12CA was localized almost exclusively to the plasma membrane and filopodia, like nsP1 alone, whereas P12CA3 and P12CA34 were found on cytoplasmic vesicles, some of which contained late endosomal markers. In immunoelectron microscopy these vesicles resembled CPVs in SFV-infected cells. Our results indicate that the nsP1 domain alone is responsible for the membrane association of the nonstructural polyprotein, whereas the nsP1 domain together with the nsP3 domain targets it to the intracellular vesicles.

scholarly journals Template-Dependent Initiation of Sindbis Virus RNA Replication In Vitro

1998 ◽  
Vol 72 (8) ◽  
pp. 6546-6553 ◽  
Author(s):  
Julie A. Lemm ◽  
Anders Bergqvist ◽  
Carol M. Read ◽  
Charles M. Rice
Keyword(s):  
Rna Polymerase ◽  
Sindbis Virus ◽  
Rna Synthesis ◽  
Rna Replication ◽  
Functional Assay ◽  
Minus Strand ◽  
Virus Rna ◽  
A Genome ◽  
Strand Initiation

ABSTRACT Recent insights into the early events in Sindbis virus RNA replication suggest a requirement for either the P123 or P23 polyprotein, as well as mature nsP4, the RNA-dependent RNA polymerase, for initiation of minus-strand RNA synthesis. Based on this observation, we have succeeded in reconstituting an in vitro system for template-dependent initiation of SIN RNA replication. Extracts were isolated from cells infected with vaccinia virus recombinants expressing various SIN proteins and assayed by the addition of exogenous template RNAs. Extracts from cells expressing P123C>S, a protease-defective P123 polyprotein, and nsP4 synthesized a genome-length minus-sense RNA product. Replicase activity was dependent upon addition of exogenous RNA and was specific for alphavirus plus-strand RNA templates. RNA synthesis was also obtained by coexpression of nsP1, P23C>S, and nsP4. However, extracts from cells expressing nsP4 and P123, a cleavage-competent P123 polyprotein, had much less replicase activity. In addition, a P123 polyprotein containing a mutation in the nsP2 protease which increased the efficiency of processing exhibited very little, if any, replicase activity. These results provide further evidence that processing of the polyprotein inactivates the minus-strand initiation complex. Finally, RNA synthesis was detected when soluble nsP4 was added to a membrane fraction containing P123C>S, thus providing a functional assay for purification of the nsP4 RNA polymerase.

scholarly journals RNA processing bodies are disassembled during Old World alphavirus infection

2019 ◽  
Vol 100 (10) ◽  
pp. 1375-1389 ◽  
Author(s):  
Lifeng Liu ◽  
Eva Weiss ◽  
Marc D. Panas ◽  
Benjamin Götte ◽  
Stina Sellberg ◽  
...  
Keyword(s):  
Rna Processing ◽  
Nuclear Import ◽  
Semliki Forest Virus ◽  
Early Stage ◽  
Processing Bodies ◽  
Old World ◽  
P Bodies ◽  
Infected Cells ◽  
As Stress ◽  
Alphavirus Infection

RNA processing bodies (P-bodies) are non-membranous cytoplasmic aggregates of mRNA and proteins involved in mRNA decay and translation repression. P-bodies actively respond to environmental stresses, associated with another type of RNA granules, known as stress granules (SGs). Alphaviruses were previously shown to block SG induction at late stages of infection, which is important for efficient viral growth. In this study, we found that P-bodies were disassembled or reduced in number very early in infection with Semliki Forest virus (SFV) or chikungunya virus (CHIKV) in a panel of cell lines. Similar to SGs, reinduction of P-bodies by a second stress (sodium arsenite) was also blocked in infected cells. The disassembly of P-bodies still occurred in non-phosphorylatable eIF2α mouse embryonal fibroblasts (MEFs) that are impaired in SG assembly. Studies of translation status by ribopuromycylation showed that P-body disassembly is independent of host translation shutoff, which requires the phosphorylation of eIF2α in the SFV- or CHIKV-infected cells. Labelling of newly synthesized RNA with bromo-UTP showed that host transcription shutoff correlated with P-body disassembly at the same early stage (3–4 h) after infection. However, inhibition of global transcription with actinomycin D (ActD) failed to disassemble P-bodies as effectively as the viruses did. Interestingly, blocking nuclear import with importazole led to an efficient P-bodies loss. Our data reveal that P-bodies are disassembled independently from SG formation at early stages of Old World alphavirus infection and that nuclear import is involved in the dynamic of P-bodies.

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