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Questions and Answers
What is the primary function of the cytoplasmic DLP in the rotavirus replication cycle?
What is the primary function of the cytoplasmic DLP in the rotavirus replication cycle?
- To initiate the assembly phase of the replication cycle
- To catalyze the formation of viroplasm
- To enclose mRNA within the new DLPs
- To catalyze primary transcription of mRNA (correct)
Which protein complex is responsible for synthesizing the 5' cap structure of the viral mRNA in rotaviruses?
Which protein complex is responsible for synthesizing the 5' cap structure of the viral mRNA in rotaviruses?
- VP2/V3 complex
- VP1/VP3 flower complex (correct)
- VP4/VP6 complex
- DLP enzyme complex
What characterizes the mRNA produced by rotaviruses?
What characterizes the mRNA produced by rotaviruses?
- It uses a viral protein to bind instead of PABP (correct)
- It contains a poly(A) tail
- It is synthesized by the host's ribosomes
- It possesses a double-stranded structure
What occurs after a few hours in the rotavirus replication cycle?
What occurs after a few hours in the rotavirus replication cycle?
What is the structural significance of the double-layered particle (DLP) in rotavirus?
What is the structural significance of the double-layered particle (DLP) in rotavirus?
What is the primary consequence of poliovirus proteolytically degrading eIF4E?
What is the primary consequence of poliovirus proteolytically degrading eIF4E?
In rotavirus, what structure is left after the uncoating process?
In rotavirus, what structure is left after the uncoating process?
Which component is crucial for the synthesis of rotavirus nucleic acids inside the DLPs?
Which component is crucial for the synthesis of rotavirus nucleic acids inside the DLPs?
How does rotavirus utilize its mRNA for protein synthesis?
How does rotavirus utilize its mRNA for protein synthesis?
Which of the following describes the genome of minus sense (-) strand RNA viruses?
Which of the following describes the genome of minus sense (-) strand RNA viruses?
What is the role of viral NSP3 in rotavirus transcription?
What is the role of viral NSP3 in rotavirus transcription?
During rotavirus infection, what occurs as older viroplasms fuse?
During rotavirus infection, what occurs as older viroplasms fuse?
What characterizes the genome of Baltimore Class V ss(-) RNA viruses?
What characterizes the genome of Baltimore Class V ss(-) RNA viruses?
How many segments does the rotavirus genome consist of?
How many segments does the rotavirus genome consist of?
What is the primary function of the viral RdRp in negative-sense RNA viruses?
What is the primary function of the viral RdRp in negative-sense RNA viruses?
How do Class IV (+) RNA viruses typically express multiple proteins from a single genome?
How do Class IV (+) RNA viruses typically express multiple proteins from a single genome?
What is the role of the IRES in the translation of poliovirus?
What is the role of the IRES in the translation of poliovirus?
What characterizes the replication scaffolds constructed by RNA viruses?
What characterizes the replication scaffolds constructed by RNA viruses?
What is the correct order of events for the translation of viral RNA in eukaryotic cells?
What is the correct order of events for the translation of viral RNA in eukaryotic cells?
Which of the following is distinct about the genome of Class IV (+) RNA viruses?
Which of the following is distinct about the genome of Class IV (+) RNA viruses?
What happens immediately after the assembly of viral proteins in RNA viruses?
What happens immediately after the assembly of viral proteins in RNA viruses?
What prevents the recognition of viruses by the host cell's immune defenses?
What prevents the recognition of viruses by the host cell's immune defenses?
What is the function of eIF4G in the translation of viral mRNA?
What is the function of eIF4G in the translation of viral mRNA?
Which of the following is a primary component of the viral internal ribosomal entry site (IRES)?
Which of the following is a primary component of the viral internal ribosomal entry site (IRES)?
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Study Notes
RNA Virus Replication and Gene Expression
- Positive-sense (+) RNA viruses have genomes that are functional mRNAs, and may be capped and polyadenylated.
- Negative-sense (-) RNA viruses must carry RdRp in their capsid for replication to begin.
- Host cell ribosomes assemble on viral genomes to synthesize viral proteins.
- Earliest viral proteins are those needed to replicate genomes and produce RdRp.
Virus Replication Complexes (VRCs)
- Many viruses that replicate in the cytoplasm compartmentalize genome replication and protein transcription within VRCs.
- VRCs escape host defences and recognition by toll-like receptors.
- VRCs are assembled by non-structural viral proteins, viral genomes, and host lipids and proteins.
Class IV (+) RNA Viruses
- Class IV (+) RNA viruses express multiple proteins from a single genome using a polyprotein.
- Polyprotein is proteolytically processed to release individual proteins, including capsomers and RdRp.
- Immediate translation of mRNA results in synthesis of viral RdRp, which then synthesizes replicative forms and viral mRNA.
Poliovirus 5' Internal Ribosome Entry Site (IRES)
- Poliovirus uses an IRES for translation initiation.
- IRES binds to ribosomes internally in mRNA, independent of the 5' cap.
- This mechanism allows the translation of viral proteins without the need for a 5' cap.
- VPg is the protein primer for genome replication.
Cap-Dependent vs. Poliovirus Initiation Complex
- Cap-dependent initiation complex involves eIF4E binding to the 5' cap and forming a complex with PABP.
- Poliovirus initiation complex uses ITAF binding to the IRES, substituting for eIF4E.
- Polyovirus proteolytically degrades eIF4E, blocking host mRNA translation, while enabling viral mRNA translation via IRES.
Baltimore Class V (-) RNA Virus Genomes
- Class V ss(-) RNA viruses cannot directly use their genomes as mRNAs.
- These viruses package RdRp within the virion.
- Orthomyxoviridae and Paramyxoviridae are examples of Class V (-) RNA viruses.
Mononegavirales: ss(-) RNA Viruses with Non-Segmented Genomes
- Measles virus is an example of a Mononegavirales virus.
Baltimore Class III dsRNA Virus Genomes: Reoviridae
- Rotavirus is an example of a Reoviridae virus.
- Rotavirus has a triple-layered, non-enveloped icosahedral capsid.
- Rotavirus uncoating leaves a double-layered particle (DLP).
- DLP contains a segmented, linear dsRNA genome with 11 segments encoding 12 proteins.
- Each segment has a 5' cap, but no poly(A) tail.
Rotavirus Genome Replication
- Rotavirus uses a viroplasm for dsRNA synthesis.
- dsRNA genome transcription takes place inside DLPs by RdRp.
- (+)RNA serves as mRNA for protein synthesis or as templates for (-)RNA synthesis.
Rotavirus mRNA and Translation
- Rotavirus mRNA has a 5' cap but no poly(A) tail.
- NSP3 substitutes for PABP by binding to a conserved sequence at the 3' end of the viral mRNA.
Rotavirus Replication Cycle
- DLPs catalyze primary transcription, releasing capped mRNAs.
- Protein synthesis leads to the formation of viroplasms.
- Viroplasms enclose mRNA and new DLPs.
- Within DLPs (+) strand templates are copied to produce new dsRNA genomes.
- New DLPs lead to exponential increase in viral mRNA and protein.
- After several hours the virus switches from gene expression to assembly.
dsRNA Viruses: Summary
- Rotavirus has three-layered capsids surrounding a segmented dsRNA genome.
- DLP is the transcriptionally active form of rotavirus in the cytoplasm.
- DLP components include enzymes for nucleic acid synthesis and structural proteins.
- VP1/VP3 complex synthesizes the 5' cap and mRNA using dsRNA as a template.
- Viral mRNA lacks a poly(A) tail, but NSP3 binds to a conserved sequence at the 3' end, substituting for PABP.
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