Classification
The murine leukemia viruses are 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 eco, "house") are capable of infecting mouse cells in culture. Non-ecotropic MLVs may be xenotropic (from xeno, "foreign", infecting non-mouse species), polytropic or modified polytropic (infecting a range of hosts including mice). Different strains of mice may have different numbers of endogenous retroviruses, and new viruses may arise as the result of recombination of endogenous sequences.
Read more about this topic: Murine Leukemia Virus