Characterization of endogenous viral loci in five lines of white Leghorn chickens.

Five lines of chickens have been examined for the presence of DNA sequences related to the endogenous avian retrovirus. Five new loci have been identified, based upon analysis with the restriction endonucleases SacI and BamHI. One locus has been associated with the production of infectious endogenous virus. Restriction endonuclease mapping suggested a limited similarity between the flanking cellular sequences of two of these loci, ev-17 and ev-18, and several endogenous loci, including ev-1, already characterized. The data suggested that these two loci might have been generated by chromosomal duplication. Hybridization analysis with a probe containing the cellular sequences that flank ev-1, however, revealed that these flanking sequences shared no detectable homology with the cellular sequences that surround ev-17, ev-18, or nine other endogenous loci that were examined. These results are consistent with the hypothesis that several of the endogenous viral loci resulted either from independent infections of the germ line or from virus transpositions.