ABSTRACT
Normal, uninfected animal cells have an unique feature, the presence in their genome of genes (proviruses) identical or closely related to infectious exogenous retrovirus. The level of expression of these genes varies from individual to individual; from complete silence to the production of virus particles. Exogenous and endogenous virus proteins were purified from sonicated viruses passed through a Sepharose 6B column satured with 6M guanidinium hydrochloride. The presence of equivalents of antigens p27 and p19 was analysed by radioimmunoassay. The presence of endogenous virus components was investigated in CEF, heart, brain, tigh muscle and wing muscle of chicken, quail and drake. The function or significance of the proteins are not known. Immunological, hormonal and environmental factors remain to be studied