Helper virus

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colspan=2 style="text-align: center; background-color: rgb(250,250,190)" | Helper Virus
colspan=2 style="min-width:15em; text-align: center; background-color: rgb(250,250,190)" | Virus classification
Species	Various

A helper virus is a virus that enables the replication of another virus, known as a defective virus, which is unable to replicate on its own. Helper viruses provide essential functions that the defective virus lacks, allowing it to complete its life cycle.

Overview

Helper viruses are crucial in the study of virology and gene therapy. They are often used in laboratory settings to propagate defective viruses that are used as vectors for delivering genetic material into cells. The relationship between helper viruses and defective viruses is a key example of viral symbiosis.

Mechanism of Action

Helper viruses provide missing functions that defective viruses need for replication. These functions can include:

• Replication enzymes: Enzymes necessary for the replication of the viral genome.
• Structural proteins: Proteins required for the assembly of the viral capsid.
• Transcription factors: Proteins that facilitate the transcription of viral genes.

The helper virus infects the same cell as the defective virus, and its gene products complement the missing functions of the defective virus, allowing it to replicate.

Examples

Adeno-Associated Virus (AAV)

Adeno-associated virus (AAV) is a well-known example of a defective virus that requires a helper virus for replication. AAV is a member of the Parvoviridae family and the Dependoparvovirus genus. It requires co-infection with a helper virus, such as adenovirus or herpes simplex virus, to replicate.

Hepatitis D Virus (HDV)

Hepatitis D virus (HDV) is another example of a defective virus that requires a helper virus. HDV is dependent on the Hepatitis B virus (HBV) for its replication. HDV uses the surface antigen of HBV to form its own viral particles.

Applications in Gene Therapy

Helper viruses are used in gene therapy to produce viral vectors that can deliver therapeutic genes to target cells. For example, AAV vectors are produced using a helper virus system in which the necessary replication functions are provided by a helper virus or plasmid.

Safety Considerations

When using helper viruses in research and therapy, it is important to ensure that the helper virus does not cause disease or unwanted effects. Researchers often use modified helper viruses that are replication-deficient or have attenuated virulence.

Conclusion

Helper viruses play a vital role in the replication of defective viruses and have significant applications in biotechnology and medicine. Understanding the interactions between helper and defective viruses can lead to advancements in viral vector development and gene therapy.

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