RNA Viruses: Replication & Gene Expression
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Questions and Answers

What role does the double layered particle (DLP) play in the rotavirus replication cycle?

The DLP is transcriptionally active in the cytoplasm, facilitating the synthesis of mRNA and proteins necessary for viral replication.

How does the VP1/VP3 complex contribute to the rotavirus lifecycle?

The VP1/VP3 complex synthesizes the 5' cap structure and mRNA using dsRNA as a template, which is crucial for translation.

Discuss the significance of the absence of a poly(A) tail in the rotavirus mRNA.

The absence of a poly(A) tail necessitates a viral nonstructural protein to bind the 3' end of mRNA, facilitating translation initiation.

Explain the transition that occurs in the rotavirus life cycle after several hours post-infection.

<p>After a few hours, the virus transitions from gene expression and genome replication to the assembly phase of its replication cycle.</p> Signup and view all the answers

What structural characteristics of rotaviruses aid their replication?

<p>Rotaviruses have three-layered capsids surrounding a segmented dsRNA genome, which protect the viral components and facilitate effective replication.</p> Signup and view all the answers

What key feature distinguishes (+) strand RNA viruses from (-) strand RNA viruses in terms of their genome functionality?

<p>(+) strand RNA viruses have genomes that function as mRNAs, while (-) strand RNA viruses require RdRp to begin replication.</p> Signup and view all the answers

Explain the importance of RdRp during the replication of (-) strand RNA viruses.

<p>RdRp is essential as it transcribes the (-) strand genome into mRNA and synthesizes new genomes.</p> Signup and view all the answers

How do viral replication complexes (VRCs) aid RNA viruses in evading host defenses?

<p>VRCs allow compartmentalization of viral replication and transcription, helping viruses escape recognition by host immune receptors.</p> Signup and view all the answers

Discuss the significance of polyprotein processing in Class IV (+) RNA viruses.

<p>Polyprotein processing is vital as it enables the release of multiple essential proteins from a single genomic copy.</p> Signup and view all the answers

What mechanism do viruses utilize when their genomes lack a 5' cap to initiate translation?

<p>Viruses with uncapped genomes use an internal ribosome entry site (IRES) to recruit the translational machinery directly.</p> Signup and view all the answers

Describe the role of eIF4G in viral translation initiation.

<p>eIF4G serves as a docking site for initiation factors and proteins, facilitating the assembly of the translation initiation complex.</p> Signup and view all the answers

Explain how the internal ribosomal entry site (IRES) differs from cap-dependent translation initiation.

<p>IRES allows for the ribosome to bind internally to the mRNA without the need for a 5' cap, while cap-dependent initiation requires this cap structure.</p> Signup and view all the answers

What is the function of the VPg protein in the replication of certain RNA viruses?

<p>VPg acts as a protein primer for genome replication, playing a crucial role in initiating the synthesis of the viral RNA.</p> Signup and view all the answers

Describe how the immediate translation of viral proteins impacts viral replication.

<p>Immediate translation of viral proteins, particularly RdRp, is crucial for rapid replication and synthesis of new viral genomes.</p> Signup and view all the answers

How do structural adaptations of Class IV (+) RNA virus genomes facilitate protein synthesis?

<p>The distinct structures of Class IV genomes allow for the expression of multiple proteins from a single strand, typically through polyprotein processing.</p> Signup and view all the answers

How does poliovirus inhibit host mRNA translation?

<p>Poliovirus degrades eIF4E, preventing cap-dependent translation of host mRNA.</p> Signup and view all the answers

What role do virus replication compartments play during the replication of (+) strand RNA viruses?

<p>Virus replication compartments facilitate the production of mRNA and new viral genomes.</p> Signup and view all the answers

Why can the genome of minus sense (-) strand RNA viruses not be used directly as mRNA?

<p>The genome must first be transcribed into a positive sense RNA, which can then serve as mRNA.</p> Signup and view all the answers

Describe the structural composition of the rotavirus virion.

<p>Rotavirus is non-enveloped and has a triple capsid structure surrounding a segmented dsRNA genome.</p> Signup and view all the answers

What happens during the uncoating of rotavirus?

<p>Uncoating leaves a double-layered particle (DLP) that is essential for viral replication.</p> Signup and view all the answers

How does rotavirus achieve genetic reassortment?

<p>Genetic reassortment occurs when cells co-infected with different rotavirus strains mix their genome segments.</p> Signup and view all the answers

What is the function of VP1 and VP3 proteins in the DLP of rotavirus?

<p>VP1 and VP3 form the internal polymerase complex that transcribes dsRNA into capped (+)RNAs.</p> Signup and view all the answers

Which protein substitutes for PABP in viral mRNA processing in rotaviruses?

<p>Viral NSP3 substitutes for PABP by binding to the 3’ end of viral mRNA.</p> Signup and view all the answers

What is the significance of the 5’ cap in the RNA segments of rotavirus?

<p>The 5’ cap is crucial for the stability and recognition of viral mRNA by ribosomes.</p> Signup and view all the answers

Explain the transcription process of dsRNA in rotavirus.

<p>RdRp transcribes dsRNA genome into capped (+) mRNAs inside the double-layered particle.</p> Signup and view all the answers

Study Notes

RNA Viruses: Replication & Gene Expression

  • RNA viruses replicate in the cytoplasm of host cells.
  • (+)RNA viruses have genomes that function as mRNAs, often capped and polyadenylated.
  • (-)RNA viruses carry RdRp within their capsid, essential for initiating replication.
  • Host cell ribosomes translate viral genomes upon entry, producing viral proteins.
  • The first viral proteins synthesized are those needed for new genome synthesis and RdRp.

Viral Replication Complexes (VRCs)

  • Many RNA viruses compartmentalize genome replication and protein transcription within VRCs.
  • VRCs are assembled from viral proteins, genomes, and host lipids and proteins.
  • VRCs provide protection from host defenses and toll-like receptors.
  • The (+) strand genome serves as a template to synthesize (-) strand anti-genomes, which stay bound to the (+) strand.

Class IV (+) RNA Viruses

  • Class IV (+) RNA viruses utilize a single genome to express multiple proteins.
  • Eukaryotic mRNA normally encodes one protein, while (+)RNA viruses require at least two: a capsomer and an RdRp.
  • Immediate translation is critical for creating RdRp, which then synthesizes replicative forms and viral mRNA.
  • Class IV viruses encode a polyprotein that is proteolytically cleaved into multiple individual proteins, including capsomers and RdRp.

Poliovirus: 5' Internal Ribosome Entry Site (IRES)

  • Poliovirus lacks a 5' cap and uses an IRES to bind ribosomes for translation.
  • The IRES allows the ribosome to bind internally, circumventing the need for a 5' cap.
  • VPg, a viral protein, is a primer for genome replication.

Translation Initiation: eIF4G

  • eIF4G (eukaryotic initiation factor) acts as a docking site for initiation factors and proteins involved in RNA translation.

Cap-Dependent vs. Poliovirus Initiation Complexes

  • Cap-dependent translation initiation involves eIF4E binding to the 5' cap and forming a complex with PABP, leading to ribosome binding near the AUG start codon.
  • Poliovirus uses ITAF, a host protein, to bind the IRES, replacing eIF4E.
  • Poliovirus degrades eIF4E, preventing cap-dependent host mRNA translation.
  • The poliovirus IRES is a complex stem-loop structure in the 5' untranslated region (UTR).

Overview of (+)RNA Virus Replication

  • Example Viruses: Poliovirus, Hepatitis C virus
  • The IRES allows for immediate translation of the genome (1).
  • The translated polyprotein is cleaved into individual proteins (2).
  • These proteins form virus replication compartments (3).
  • Within these compartments, double-stranded replicative forms are used to produce mRNA and new genomes (4).
  • These new genomes are used to form new infectious virions (5).

Class V ss(-) RNA Viruses

  • Class V ss(-) RNA viruses may have segmented or non-segmented genomes.
  • Examples: Orthobunyaviruses, Orthomyxoviridae, Paramyxoviridae
  • (-)RNA viruses cannot directly use their genome as mRNA.
  • They package RdRp within the virion to initiate transcription.

Mononegavirales: ss(-)RNA viruses with non-segmented genomes

  • Example: Measles virus

Class III dsRNA Viruses: Reoviridae

  • Example: Rotavirus
  • Rotaviruses have a non-enveloped, icosahedral capsid with a triple-layered structure.
  • Uncoating exposes a double-layered particle (DLP).
  • Rotaviruses have a segmented, linear dsRNA genome with 11 segments encoding 12 proteins.
  • Each segment has a 5' cap, but no polyA tail.
  • Co-infection with different rotavirus strains can lead to reassortment of genome segments.

Rotavirus Genome Organization & Replication

  • The rotavirus genome is segmented, with each segment encoding a specific protein.
  • Replication occurs within viroplasms, cytoplasmic structures formed during infection.
  • The DLP contains the viral RdRp, VP1/VP3, which transcribes capped (+)RNAs from each segment.
  • These (+)RNAs function as mRNAs for protein synthesis and templates for (-)RNA synthesis.
  • DLPs are fenestrated, allowing entry of NTPs and exit of newly synthesized mRNA.

Rotavirus mRNA: Translation Initiation

  • Rotavirus mRNA has a 5' cap but lacks a polyA tail.
  • Viral nonstructural protein NSP3 binds to a conserved sequence near the 3' end of mRNA, substituting for PABP.
  • This allows for efficient translation of viral mRNA.

Rotavirus Replication Cycle: Summary

  • The DLP catalyzes primary transcription, producing capped mRNA (1).
  • Translated proteins form viroplasms, encapsulating mRNA with new DLPs (2).
  • Inside new DLPs, (+)RNA templates are copied, forming DLPs with dsRNA genomes (3).
  • This process leads to exponential increases in viral mRNA and protein (4).
  • After a few hours, the virus switches from transcription and replication to assembly (5).

dsRNA Viruses: Key Points

  • Rotaviruses have three-layered capsids surrounding a segmented dsRNA genome.
  • The DLP is the transcriptionally active form of rotavirus.
  • Many DLP components are enzymes involved in nucleic acid synthesis and structural proteins.
  • VP1/VP3, a structural protein, synthesizes the 5' cap and mRNA using dsRNA as a template.
  • Rotavirus mRNA lacks a polyA tail, but NSP3 binds to a conserved sequence near the 3' end, replacing PABP.

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RNA Virus Replication PDF

Description

Explore the intricate processes of RNA virus replication and gene expression. Learn about the roles of (+) and (-) RNA viruses, the significance of viral replication complexes (VRCs), and how these viruses utilize their genomes to express multiple proteins. Test your understanding of the complexities involved in RNA viral biology.

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