Difference Between Provirus and Retrovirus

The key difference between provirus and retrovirus is that provirus is a stage of viral replication which shows the integrated state of viral genome with host genome while retrovirus is an RNA virus that has the ability to convert its RNA genome into DNA intermediate by enzyme reverse transcriptase.

Viruses are tiny infectious particles that are able to replicate inside a living organism. Therefore, they are obligate intracellular parasites. They can infect almost all living organisms, including animals, plants, fungi, protozoa and bacteria. Thus, they are the causative agents of many deadly diseases, including HIV, polio, rubella, hepatitis, etc. Furthermore, they are microscopic particles composed of protein capsids and DNA or RNA genome. Their genome can be single-stranded or double-stranded, circular or linear. Retrovirus is a group of viruses. These viruses possess a positive-sense single-stranded RNA genome and genes coding for reverse transcriptase enzyme. Hence, they are capable of replicating via an intermediate of DNA. In contrast, the provirus is a stage of viral replication.

CONTENTS

1. Overview and Key Difference
2. What is Provirus 
3. What is Retrovirus
4. Similarities Between Provirus and Retrovirus
5. Side by Side Comparison – Provirus vs Retrovirus in Tabular Form
6. Summary

What is Provirus?

A provirus is a stage of viral replication inside the host. In this stage, the virus genome exists integrated with the host genome. Generally, provirus refers to a viral genome inserted into genomic DNA of a eukaryotic host cell. Proviruses and prophages are similar structures, but provirus differs from prophage due to that fact that provirus integrates the viral genome into a eukaryotic genome while prophage selects bacterial genome as their host. Provirus can act as an endogenous viral element for longer periods of time, which has the potential of causing infection. The common example is endogenous retroviruses which are always present in a stage of the provirus.

Proviruses undergo lysogenic viral replication. Once the provirus is integrated into the host genome, it does not replicate by itself; it replicates with the eukaryotic host genome. Through this process, the provirus will pass onto the original cell and, through cell division, the provirus will be present in all descendant cells of the initially infected cell.

Furthermore, provirus integration to the eukaryotic genome can result in two types of infection; latent infection and productive infection. Latent infection occurs when the provirus gets transcriptionally silent. During productive infection, the integrated provirus becomes transcriptionally active and transcribes into mRNA (messenger RNA), which results in the direct production of a new virus. The produced viruses come out disrupting the cell membranes. A latent infection has the potential to become a productive infection if the organism gets immune-compromised or due to certain other health issues.

What is Retrovirus?

A retrovirus is a viral group which possesses a positive-sense single-stranded RNA genome. They contain an enzyme called reverse transcriptase and their replication occurs via a DNA intermediate. The production of an intermediate DNA during the replication is unique to this group of viruses.

During the infection, retroviruses attach to the host cell through the specific glycoproteins located at the outer surface of the viral particle. They fuse with the cell membrane and enter the host cell. After penetration into the host cell cytoplasm, retrovirus reverse transcribes its genome into double-stranded DNA using reverse transcriptase enzyme. The new DNA integrates into the host cell genome using an enzyme called integrase and produces the provirus stage. Though an infection has occurred, the host cell fails to recognize viral DNA after integration. Hence, during the host genome replication, viral genome replicates and produces necessary proteins to make new copies of viral particles.

Retroviruses can be transmitted by direct contact between two human subjects or between two animals. There are three retroviruses families: Oncovirus, Lentivirus and Spumavirus. Oncoviruses are viruses that cause the development of cancers. Lentiviruses are the viruses that lead to the onset of deadly infectious diseases, whereas Spumavirus contains characteristic spikes radiating from the envelope.

Diseases associated with retroviral infection include feline leukaemia or sarcoma, caprine arthritis encephalitis, human adult cell leukaemia, etc. Due to their natural ability to insert the viral genome inside the host organisms, retroviruses have an immense use in gene delivery systems, and they act as valuable research tools in molecular biology.

What are the Similarities Between Provirus and Retrovirus?

• Retroviruses replication occurs via a provirus stage.
• Therefore, the provirus is a critical stage of retroviral multiplication.

What is the Difference Between Provirus and Retrovirus?

A provirus is a viral genome integrated with the host genome and is a stage of viral replication. In contrast, a retrovirus is an RNA virus that is able to reverse transcribe its RNA genome into DNA prior to integration with the host genome. So, this is the key difference between provirus and retrovirus. Retroviruses contain reverse transcriptase enzymes, unlike provirus.

Summary – Provirus vs Retrovirus

A provirus is a stage of viral replication. It is the viral genome integrated into the host genome. In contrast, a retrovirus is a single-stranded RNA virus which replicates via a DNA intermediate. So, this is the key difference between provirus and retrovirus. Retroviruses also undergo provirus stage during their replication within the host.

Reference:

1. Coffin, John M. “Transcription.” Retroviruses., U.S. National Library of Medicine, 1 Jan. 1997, Available here.
2. “Provirus.” Wikipedia, Wikimedia Foundation, 8 Oct. 2018, Available here.

Image Courtesy:

1. “12981 2016 114 Fig2 HTML” By Mofeeddaban – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Hiv gross” By Translated by Raul654 – Originally from GFDL image Image:Hiv gross german.png (CC BY-SA 3.0) via Commons Wikimedia