The Roles of Pol and Env in the Assembly Pathway of Human Foamy Virus

ABSTRACT Human foamy virus (HFV) is the prototype of theSpumavirus genus of retroviruses. These viruses have a genomic organization close to that of other complex retroviruses but have similarities to hepadnaviruses such as human hepatitis B virus (HBV). Both HFV and HBV express their Pol protein independently of their structural proteins. Retroviruses and hepadnaviruses differ in their requirements for particle assembly and genome packaging. Assembly of retroviral particles containing RNA genomes requires only the Gag structural protein. The Pol protein is not required for capsid assembly, and the Env surface glycoprotein is not required for release of virions from the cell. In contrast, assembly of extracellular HBV particles containing DNA requires core structural protein and polymerase (P protein) for assembly of nucleocapsids and requires surface glycoproteins for release from the cell. We investigated the requirements for synthesis of extracellular HFV particles by constructing mutants with either the pol or envgene deleted. We found that the Pol protein is dispensable for production of extracellular particles containing viral nucleic acid. In the absence of Env, intracellular particles are synthesized but few or no extracellular particles could be detected. Thus, foamy virus assembly is distinct from that of other reverse transcriptase-encoding mammalian viruses.

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Alix-Mediated Rescue of Feline Immunodeficiency Virus Budding Differs from That Observed with Human Immunodeficiency Virus

Journal of Virology ◽

10.1128/jvi.02019-19 ◽

2020 ◽

Vol 94 (11) ◽

Author(s):

Claudia Del Vecchio ◽

Michele Celestino ◽

Marta Celegato ◽

Giorgio Palù ◽

Cristina Parolin ◽

...

Keyword(s):

Human Immunodeficiency Virus ◽

Feline Immunodeficiency Virus ◽

Virus Assembly ◽

Cellular Protein ◽

Structural Protein ◽

Virus Budding ◽

Particle Assembly ◽

Gag Protein ◽

Double Mutation ◽

Immunodeficiency Virus

ABSTRACT The structural protein Gag is the only viral component required for retroviral budding from infected cells. Each of the three conserved domains—the matrix (MA), capsid (CA), and nucleocapsid (NC) domains—drives different phases of viral particle assembly and egress. Once virus assembly is complete, retroviruses, like most enveloped viruses, utilize host proteins to catalyze membrane fission and to free progeny virions. These proteins are members of the endosomal sorting complex required for transport (ESCRT), a cellular machinery that coats the inside of budding necks to perform membrane-modeling events necessary for particle abscission. The ESCRT is recruited through interactions with PTAP and LYPXnL, two highly conserved sequences named late (L) domains, which bind TSG101 and Alix, respectively. A TSG101-binding L-domain was identified in the p2 region of the feline immunodeficiency virus (FIV) Gag protein. Here, we show that the human protein Alix stimulates the release of virus from FIV-expressing human cells. Furthermore, we demonstrate that the Alix Bro1 domain rescues FIV mutants lacking a functional TSG101-interacting motif, independently of the entire p2 region and of the canonical Alix-binding L-domain(s) in FIV Gag. However, in contrast to the effect on human immunodeficiency virus type 1 (HIV-1), the C377,409S double mutation, which disrupts both CCHC zinc fingers in the NC domain, does not abrogate Alix-mediated virus rescue. These studies provide insight into conserved and divergent mechanisms of lentivirus-host interactions involved in virus budding. IMPORTANCE FIV is a nonprimate lentivirus that infects domestic cats and causes a syndrome that is reminiscent of AIDS in humans. Based on its similarity to HIV with regard to different molecular and biochemical properties, FIV represents an attractive model for the development of strategies to prevent and/or treat HIV infection. Here, we show that the Bro1 domain of the human cellular protein Alix is sufficient to rescue the budding of FIV mutants devoid of canonical L-domains. Furthermore, we demonstrate that the integrity of the CCHC motifs in the Gag NC domain is dispensable for Alix-mediated rescue of virus budding, suggesting the involvement of other regions of the Gag viral protein. Our research is pertinent to the identification of a conserved yet mechanistically divergent ESCRT-mediated lentivirus budding process in general, and to the role of Alix in particular, which underlies the complex viral-cellular network of interactions that promote late steps of the retroviral life cycle.

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Nucleic Acid Binding by Mason-Pfizer Monkey Virus CA Promotes Virus Assembly and Genome Packaging

Journal of Virology ◽

10.1128/jvi.03197-15 ◽

2016 ◽

Vol 90 (9) ◽

pp. 4593-4603 ◽

Cited By ~ 7

Author(s):

Tibor Füzik ◽

Růžena Píchalová ◽

Florian K. M. Schur ◽

Karolína Strohalmová ◽

Ivana Křížová ◽

...

Keyword(s):

Nucleic Acid ◽

Protein Interactions ◽

Viral Genome ◽

Virus Assembly ◽

Protein Protein Interactions ◽

Genome Packaging ◽

Particle Assembly ◽

Nuclear Trafficking ◽

Virus Particles ◽

Gag Polyprotein

ABSTRACTThe Gag polyprotein of retroviruses drives immature virus assembly by forming hexameric protein lattices. The assembly is primarily mediated by protein-protein interactions between capsid (CA) domains and by interactions between nucleocapsid (NC) domains and RNA. Specific interactions between NC and the viral RNA are required for genome packaging. Previously reported cryoelectron microscopy analysis of immature Mason-Pfizer monkey virus (M-PMV) particles suggested that a basic region (residues RKK) in CA may serve as an additional binding site for nucleic acids. Here, we have introduced mutations into the RKK region in both bacterial and proviral M-PMV vectors and have assessed their impact on M-PMV assembly, structure, RNA binding, budding/release, nuclear trafficking, and infectivity usingin vitroandin vivosystems. Our data indicate that the RKK region binds and structures nucleic acid that serves to promote virus particle assembly in the cytoplasm. Moreover, the RKK region appears to be important for recruitment of viral genomic RNA into Gag particles, and this function could be linked to changes in nuclear trafficking. Together these observations suggest that in M-PMV, direct interactions between CA and nucleic acid play important functions in the late stages of the viral life cycle.IMPORTANCEAssembly of retrovirus particles is driven by the Gag polyprotein, which can self-assemble to form virus particles and interact with RNA to recruit the viral genome into the particles. Generally, the capsid domains of Gag contribute to essential protein-protein interactions during assembly, while the nucleocapsid domain interacts with RNA. The interactions between the nucleocapsid domain and RNA are important both for identifying the genome and for self-assembly of Gag molecules. Here, we show that a region of basic residues in the capsid protein of the betaretrovirus Mason-Pfizer monkey virus (M-PMV) contributes to interaction of Gag with nucleic acid. This interaction appears to provide a critical scaffolding function that promotes assembly of virus particles in the cytoplasm. It is also crucial for packaging the viral genome and thus for infectivity. These data indicate that, surprisingly, interactions between the capsid domain and RNA play an important role in the assembly of M-PMV.

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Evidence that the Human Foamy Virus Genome Is DNA

Journal of Virology ◽

10.1128/jvi.73.2.1565-1572.1999 ◽

1999 ◽

Vol 73 (2) ◽

pp. 1565-1572 ◽

Cited By ~ 95

Author(s):

Shuyuarn F. Yu ◽

Mark D. Sullivan ◽

Maxine L. Linial

Keyword(s):

Viral Replication ◽

Foamy Virus ◽

Transcriptase Inhibitor ◽

Virus Genome ◽

Human Foamy Virus ◽

Extracellular Virus ◽

Double Stranded Dna ◽

Viral Particles ◽

B Virus ◽

Reverse Transcriptase Inhibitor

ABSTRACT The genomes of the spumaviruses, of which human foamy virus (HFV) is the prototype, are very similar to those of other complex retroviruses. However, in some aspects of the viral replicative cycle, HFV more closely resembles pararetroviruses such as hepatitis B virus. Previous work indicated that HFV extracellular particles contain apparently full-length double-stranded DNA, as well as RNA. We have further characterized the amount of DNA in particles and the role that this DNA has in viral replication. Experiments with the reverse transcriptase inhibitor 3′-azido-3′-deoxythymidine (AZT) suggest that reverse transcription is largely complete before extracellular virus infects new cells. In addition, we have been able to show that DNA extracted from virions can lead to production of virus after transfection. Taken together, these data suggest that complete, or nearly complete, proviral-length DNA is present in viral particles and that this DNA is sufficient for new rounds of viral replication.

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Interactions between HIV-1 Gag and Viral RNA Genome Enhance Virion Assembly

Journal of Virology ◽

10.1128/jvi.02319-16 ◽

2017 ◽

Vol 91 (16) ◽

Cited By ~ 13

Author(s):

Kari A. Dilley ◽

Olga A. Nikolaitchik ◽

Andrea Galli ◽

Ryan C. Burdick ◽

Louis Levine ◽

...

Keyword(s):

Particle Production ◽

High Efficiency ◽

Virus Assembly ◽

Viral Rna ◽

Structural Protein ◽

Genome Packaging ◽

Virion Assembly ◽

Rna Genome ◽

Hiv 1 ◽

In Cells

ABSTRACT Most HIV-1 virions contain two copies of full-length viral RNA, indicating that genome packaging is efficient and tightly regulated. However, the structural protein Gag is the only component required for the assembly of noninfectious viruslike particles, and the viral RNA is dispensable in this process. The mechanism that allows HIV-1 to achieve such high efficiency of genome packaging when a packageable viral RNA is not required for virus assembly is currently unknown. In this report, we examined the role of HIV-1 RNA in virus assembly and found that packageable HIV-1 RNA enhances particle production when Gag is expressed at levels similar to those in cells containing one provirus. However, such enhancement is diminished when Gag is overexpressed, suggesting that the effects of viral RNA can be replaced by increased Gag concentration in cells. We also showed that the specific interactions between Gag and viral RNA are required for the enhancement of particle production. Taken together, these studies are consistent with our previous hypothesis that specific dimeric viral RNA-Gag interactions are the nucleation event of infectious virion assembly, ensuring that one RNA dimer is packaged into each nascent virion. These studies shed light on the mechanism by which HIV-1 achieves efficient genome packaging during virus assembly. IMPORTANCE Retrovirus assembly is a well-choreographed event, during which many viral and cellular components come together to generate infectious virions. The viral RNA genome carries the genetic information to new host cells, providing instructions to generate new virions, and therefore is essential for virion infectivity. In this report, we show that the specific interaction of the viral RNA genome with the structural protein Gag facilitates virion assembly and particle production. These findings resolve the conundrum that HIV-1 RNA is selectively packaged into virions with high efficiency despite being dispensable for virion assembly. Understanding the mechanism used by HIV-1 to ensure genome packaging provides significant insights into viral assembly and replication.

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Delayed by Design: Role of Suboptimal Signal Peptidase Processing of Viral Structural Protein Precursors in Flaviviridae Virus Assembly

Viruses ◽

10.3390/v12101090 ◽

2020 ◽

Vol 12 (10) ◽

pp. 1090

Author(s):

Nabeel Alzahrani ◽

Ming-Jhan Wu ◽

Saravanabalaji Shanmugam ◽

MinKyung Yi

Keyword(s):

Virus Assembly ◽

Signal Peptidase ◽

Structural Protein ◽

Nonstructural Proteins ◽

Particle Assembly ◽

Virus Family ◽

Viral Structural Protein ◽

Replication Scheme ◽

Viral Polyprotein

The Flaviviridae virus family is classified into four different genera, including flavivirus, hepacivirus, pegivirus, and pestivirus, which cause significant morbidity and mortality in humans and other mammals, including ruminants and pigs. These are enveloped, single-stranded RNA viruses sharing a similar genome organization and replication scheme with certain unique features that differentiate them. All viruses in this family express a single polyprotein that encodes structural and nonstructural proteins at the N- and C-terminal regions, respectively. In general, the host signal peptidase cleaves the structural protein junction sites, while virus-encoded proteases process the nonstructural polyprotein region. It is known that signal peptidase processing is a rapid, co-translational event. Interestingly, certain signal peptidase processing site(s) in different Flaviviridae viral structural protein precursors display suboptimal cleavage kinetics. This review focuses on the recent progress regarding the Flaviviridae virus genus-specific mechanisms to downregulate signal peptidase-mediated processing at particular viral polyprotein junction sites and the role of delayed processing at these sites in infectious virus particle assembly.

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Effective inhibition of hepatitis B virus replication by small interfering RNAs expressed from human foamy virus vectors

International Journal of Molecular Medicine ◽

10.3892/ijmm.19.4.705 ◽

2007 ◽

Cited By ~ 1

Author(s):

Yan Sun ◽

Zhi Li ◽

Lijun Li ◽

Jing Li ◽

Xiaobo Liu ◽

...

Keyword(s):

Hepatitis B Virus ◽

Hepatitis B ◽

Virus Replication ◽

Foamy Virus ◽

Human Foamy Virus ◽

Small Interfering Rnas ◽

Virus Vectors ◽

B Virus ◽

Effective Inhibition

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Dynamic Association between HIV-1 Gag and Membrane Domains

Molecular Biology International ◽

10.1155/2012/979765 ◽

2012 ◽

Vol 2012 ◽

pp. 1-13 ◽

Cited By ~ 12

Author(s):

Ian B. Hogue ◽

G. Nicholas Llewellyn ◽

Akira Ono

Keyword(s):

Plasma Membrane ◽

Virus Assembly ◽

Active Role ◽

Spherical Particles ◽

Cell Junction ◽

Membrane Microdomains ◽

Virological Synapse ◽

Structural Protein ◽

Particle Assembly ◽

Hiv 1

HIV-1 particle assembly is driven by the structural protein Gag. Gag binds to and multimerizes on the inner leaflet of the plasma membrane, eventually resulting in formation of spherical particles. During virus spread among T cells, Gag accumulates to the plasma membrane domain that, together with target cell membrane, forms a cell junction known as the virological synapse. While Gag association with plasma membrane microdomains has been implicated in virus assembly and cell-to-cell transmission, recent studies suggest that, rather than merely accumulating to pre-existing microdomains, Gag plays an active role in reorganizing the microdomains via its multimerization activity. In this paper, we will discuss this emerging view of Gag microdomain interactions. Relationships between Gag multimerization and microdomain association will be further discussed in the context of Gag localization to T-cell uropods and virological synapses.

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