MMLV

Murine leukemia virus
Virus classification
Group:	Group VI (ssRNA-RT)
Order:	Unassigned
Family:	Retroviridae
Subfamily:	Orthoretrovirinae
Genus:	Gammaretrovirus
Species:	Murine leukemia virus

The murine leukemia viruses (MLVs or MuLVs) are retroviruses named for their ability to cause cancer in murine (mouse) hosts. Some MLVs may infect other vertebrates. MLVs include both exogenous and endogenous viruses. Replicating MLVs have a positive sense, single-stranded RNA (ssRNA) genome that replicates through a DNA intermediate via the process of reverse transcription.

The murine leukemia viruses are group/type VI retroviruses belonging to the gammaretroviral genus of the Retroviridae family. The viral particles of replicating MLVs have C-type morphology as determined by electron microscopy.

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.

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. 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. Different strains of mice may have different numbers of endogenous retroviruses, and new viruses may arise as the result of recombination of endogenous sequences.

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