Organization of Endogenous Retrovirus Genes
In mammals virogenes are multiple copy elements. Estimates of the number of copies lie between five and several hundred. This wide range results from variations in the copy number of different virogenes and from technieal considerations. The conventional means for determining the number of copies of a particular gene in mammalian DNA is to follow the kinetics of hybridization of labeled RNA or cDNA copies of the gene to a vast excess of unlabeled cell DNA. Under this condition the rate of hybridization of the labeled probe, or more properly the half-life of the unreacted probe, is dependent on the concentration of complementary sequences in the cell DNA (Britten and Kohne, 1968). The condition under which half of the viral probe hybridizes, the C0t½, is related to the number of copies of virogenes per haploid genome. Actually, assigning a copy number depends on knowing: (1) the degree of divergence between the viral probe and the virogenes, (2) that the viral probe does not react with nonviral sequences in the cell DNA, and (3) the kinetics of hybridization of a single-copy standard.
KeywordsHybridization Solution Buoyant Density Rous Sarcoma Virus Molecular Hybridization Feline Leukemia Virus
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