Murine leukemia virus
Murine leukemia virus | |
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Virus classification | |
(unranked): | Virus |
Realm: | Riboviria |
Kingdom: | Pararnavirae |
Phylum: | Artverviricota |
Class: | Revtraviricetes |
Order: | Ortervirales |
Family: | Retroviridae |
Genus: | Gammaretrovirus |
Species: | Murine leukemia virus
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The murine leukemia viruses (MLVs or MuLVs) are
Classification
The murine leukemia viruses are
The MLVs include both exogenous and endogenous viruses. Exogenous forms are transmitted as new infections from one host to another. The Moloney, Rauscher, Abelson and Friend MLVs, named for their discoverers, are used in cancer research.[citation needed]
Endogenous MLVs are integrated into the host's germ line and are passed from one generation to the next. Stoye and Coffin have classified them into four categories by host specificity, determined by the genomic sequence of their envelope region.[1] The ecotropic MLVs (from Gr.eco, "Home") are capable of infecting mouse cells in culture. Non-ecotropic MLVs may be xenotropic (from xenos, "foreign", infecting non-mouse species), polytropic or modified polytropic (infecting a range of hosts including mice). Among the latter MLVs are amphotropic viruses (Gr. amphos, "both") that can infect both mouse cells and cells of other animal species. These terms and descriptions for the MLV biologic classification were initially introduced by Levy.[2] Different strains of mice may have different numbers of endogenous retroviruses, and new viruses may arise as the result of recombination of endogenous sequences.[3][4]
Virion structure
As Type C
Genome
The genomes of exogenous and endogenous murine leukemia viruses have been fully sequenced. The viral genome is a single stranded, positive-sense RNA highly folded, molecule of around 8000 nucleotides. From 5' to 3' (typically displayed as "left" to "right"), the genome contains gag, pol, and env regions, coding for structural proteins, enzymes including the RNA-dependent DNA polymerase (reverse transcriptase), and coat proteins, respectively. In addition to these three polyproteins: Gag, Pol and Env, common to all retroviruses, MLV also produces the p50/p60 proteins issued from an alternative splicing of its genomic RNA..[6] The genomic molecule contains a 5' methylated cap structure and a 3' poly-adenosine tail.[citation needed]
The genome includes a conserved RNA structural element called a
Replication cycle
Infection begins when the surface glycoprotein (SU) on the outer part of the mature, infectious virion binds to the receptor on the surface of the new host cell. As a result of attachment, changes occur in Env. These changes lead to the release of the surface glycoprotein (SU) and the conformational rearrangement of the transmembrane protein (TM). As a result, the fusion of the viral membrane and the plasma membrane occurs. Fusion of the membranes leads to the deposition of the virion content in the cytoplasm of the cell. After entering the cytoplasm, viral RNA is copied into a single dsDNA molecule by reverse transcriptase. This DNA is somehow carried into the nucleus, where the integrase (IN) protein catalyzes its insertion into chromosomal DNA. The viral DNA integrated into the host genome is called “provirus”. It is copied and translated by normal host-cell machinery. The encoded proteins are trafficked to the plasma membrane, where they assemble into progeny virus particles. Immature particles are released from the cell with the help of cellular "ESCRT" machinery and then they undergo maturation as the viral protease cleaves the polyproteins. The particle cannot start a new infection until maturation occurs.[10]
Viral evolution
As with other retroviruses, the MLVs replicate their genomes with relatively low fidelity. Thus,
Research
The
Application
- Gene therapy: MLV-derived particles can deliver therapeutic genes to target cells.
- Cancer studies: MLVs are used to study cancer development.
- As a model retrovirus in viral clearance studies
- Reverse transcriptase from MMLV is used in biotechnology
References
Further reading
- Wood KJ, Fry J (June 1999). "Gene therapy: potential applications in clinical transplantation". Expert Reviews in Molecular Medicine. 1999 (11): 1–20. S2CID 26836701.)
Table 1. A comparison of vectors in use for clinical gene transfer
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- Sliva K, Erlwein O, Bittner A, Schnierle BS (December 2004). "Murine leukemia virus (MLV) replication monitored with fluorescent proteins". Virology Journal. 1: 14. PMID 15610559.