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Viruses with RNA Genomes

Viruses with RNA Genomes

RNA viruses are categorized into positive-strand, negative-strand, or double-stranded groups based on their genomic structure and replication mechanisms. This classification dictates how they exploit host cellular machinery for protein synthesis and replication. Some RNA viruses also utilize reverse transcription as part of their life cycle, further diversifying their replication strategies.Positive-Strand RNA VirusesPositive-strand RNA viruses have genomes that function directly as messenger...

Retroviruses

Retroviruses

Retroviruses and retrotransposons both insert copies of their genetic elements into the genome of the host cell. Thus, the viral genes are passed on when the host genome is replicated or translated. A typical retroviral DNA sequence contains 3-4 genes that encode the different proteins required for its structural assembly and function as a molecular parasite. This DNA is transcribed into a single mRNA, which is very similar in structure to conventional mRNAs, i.e., it is capped at the 5’...

Viral Structure

Viral Structure

Viruses are extraordinarily diverse in shape and size, but they all have several structural features in common. All viruses have a core that contains a DNA- or RNA-based genome. The core is surrounded by a protective coat of proteins called the capsid. The capsid is composed of subunits called capsomeres. The capsid and genome-containing core are together known as the nucleocapsid.

Retrovirus Life Cycles

Retrovirus Life Cycles

Retroviruses have a single-stranded RNA genome that undergoes a special form of replication. Once the retrovirus has entered the host cell, an enzyme called reverse transcriptase synthesizes double-stranded DNA from the retroviral RNA genome. This DNA copy of the genome is then integrated into the host’s genome inside the nucleus via an enzyme called integrase. Consequently, the retroviral genome is transcribed into RNA whenever the host’s genome is transcribed, allowing the...

Leaky Scanning

Leaky Scanning

During most eukaryotic translation processes, the small 40S ribosome subunit scans an mRNA from its 5' end until it encounters the first start AUG codon. The large 60S ribosomal subunit then joins the smaller one to initiate protein synthesis. The location of the translation initiation is largely determined by the nucleotides near the start codon as there may be multiple translation initiation sites present on the mRNA. Marilyn Kozak discovered that the sequence RCCAUGG (where R...

Subviral Agents

Subviral Agents

Subviral agents are infectious entities that resemble viruses but lack one or more viral components, such as a capsid or essential replication machinery. These agents include viroids, prions, and satellites, each possessing distinct structural and functional characteristics that influence their mode of infection and replication.Viroids are the simplest subviral agents, consisting of circular, single-stranded RNA molecules without a protein coat. They exclusively infect plants, relying entirely...

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Combining Analysis of DNA in a Crude Virion Extraction with the Analysis of RNA from Infected Leaves to Discover New Virus Genomes

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Picornaviruses: A View from 3A.

Terry Jackson¹, Graham J Belsham²

¹The Pirbright Institute, Pirbright, Woking, Surrey GU24 0NF, UK.

|April 3, 2021

Summary

Picornavirus 3A proteins are key to viral replication, influencing host interactions and host range. This review clarifies their diverse roles and challenges in the picornavirus life cycle.

Keywords:

RNA replication lipid droplets membrane interactions phosphatidylinositol 4-kinase protein interactions protein trafficking replication organelles virus host-range virus replication

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Last Updated: Nov 10, 2025

Combining Analysis of DNA in a Crude Virion Extraction with the Analysis of RNA from Infected Leaves to Discover New Virus Genomes

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Published on: July 27, 2018

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Published on: March 2, 2016

Area of Science:

Virology
Molecular Biology
Genetics

Background:

Picornaviruses possess a positive-sense RNA genome within a protein capsid.
They cause significant human and animal diseases.
Viral replication relies on non-structural proteins, including RNA-dependent RNA polymerase (3Dpol) and accessory proteins like 3A.

Purpose of the Study:

To revisit and clarify the multifaceted roles of picornavirus 3A proteins.
To discuss the distinct functions of the 3AB precursor and mature 3A.
To address recent findings that challenge established roles of 3A proteins.

Main Methods:

Literature review of existing research on picornavirus 3A proteins.
Analysis of conserved and divergent functions across picornavirus genera.
Comparison of roles assigned to 3A versus potential roles of 3AB.

Main Results:

3A proteins exhibit significant divergence across picornaviruses, impacting replication and host interactions.
They are involved in generating replication organelles and modulating host cellular functions.
3A proteins influence viral replication efficiency, host response, and host range determination.

Conclusions:

The functions of 3A proteins are complex and vary between picornavirus genera.
Recent evidence suggests some previously attributed roles may be performed by other viral proteins.
Distinguishing the roles of 3AB and 3A is crucial for understanding the picornavirus life cycle.