Mason-Pfizer monkey virus

Mason-Pfizer Monkey Virus (MPMV)

Mason-Pfizer Monkey Virus (MPMV) is a type of betaretrovirus that was first isolated from a rhesus macaque in 1970. It is a member of the Retroviridae family and is known for its ability to cause simian AIDS in monkeys. MPMV is often studied as a model for understanding retroviral replication and pathogenesis.

Genome Structure

The genome of Mason-Pfizer Monkey Virus is a single-stranded, positive-sense RNA molecule. Like other retroviruses, MPMV has a genome that is approximately 8.3 kilobases in length. The genome is flanked by long terminal repeats (LTRs) at both ends, which play crucial roles in the integration of the viral genome into the host cell's DNA and in the regulation of viral gene expression.

Genomic Organization

The MPMV genome is organized into several key regions, each encoding different viral proteins necessary for the virus's life cycle:

• Gag (Group-specific antigen): This region encodes the structural proteins of the virus, including the matrix, capsid, and nucleocapsid proteins. These proteins are essential for the assembly and maturation of viral particles.

• Pol (Polymerase): The pol region encodes the enzymes required for viral replication, including reverse transcriptase, integrase, and protease. Reverse transcriptase is responsible for converting the viral RNA genome into DNA, which can then be integrated into the host genome by integrase.

• Env (Envelope): This region encodes the envelope glycoproteins, which are involved in the virus's ability to infect host cells. The envelope proteins facilitate the binding and entry of the virus into the host cell.

• Rev and Tat: These are regulatory proteins that play roles in the regulation of viral gene expression and replication. Rev is involved in the export of unspliced and singly spliced viral mRNA from the nucleus to the cytoplasm, while Tat enhances the transcription of viral genes.

Unique Features

One of the unique features of the MPMV genome is the presence of a cis-acting element known as the "constitutive transport element" (CTE). The CTE is located within the 3' untranslated region (UTR) of the viral RNA and is crucial for the nuclear export of unspliced viral RNA. This element allows the virus to bypass the host cell's normal mRNA splicing and export mechanisms, facilitating the production of viral proteins necessary for replication.

Replication Cycle

The replication cycle of MPMV begins with the binding of the viral envelope proteins to specific receptors on the surface of the host cell. Following entry into the cell, the viral RNA genome is reverse transcribed into DNA by the viral reverse transcriptase enzyme. The resulting DNA is then integrated into the host cell's genome by the integrase enzyme, forming a provirus.

Once integrated, the provirus can be transcribed by the host cell's machinery to produce new viral RNA genomes and mRNA for viral protein synthesis. The newly synthesized viral components are assembled into immature viral particles, which then bud from the host cell. During or after budding, the viral protease cleaves the Gag and Gag-Pol polyproteins, leading to the maturation of the viral particles into infectious virions.

See Also

• Retrovirus
• Simian immunodeficiency virus
• Viral replication

References

• Coffin, J. M., Hughes, S. H., & Varmus, H. E. (1997). Retroviruses. Cold Spring Harbor Laboratory Press.
• Temin, H. M., & Mizutani, S. (1970). RNA-dependent DNA polymerase in virions of Rous sarcoma virus. Nature, 226(5252), 1211-1213.

External Links

• [Retroviridae - ICTVdB - The Universal Virus Database]
• [Retroviruses - Cold Spring Harbor Laboratory Press]