Endogenous proviruses of random-bred chickens and ring-necked pheasants: analysis with restriction endonucleases

We have examined, by digestion with restriction endonucleases and nucleic acid hybridization, sequences homologous to avian sarcoma virus (ASV) DNA in DNA from 18 random-bred chickens of the brown leghorn and brown nick flocks and 8 ring-necked pheasants. Both species have sequences related to the replicative genes (gag, pol, andenv) and to the transforming gene (src) of ASV. The disposition of these sequences in random-bred chickens is reminiscent of the situation in inbred white leghorn flocks; the sequences related togag, pol, andenv appear to reside in structures which closely resemble proviruses of the endogenous chicken virus RAV-O, and thesrc-related sequences appear to be a cellular gene (or genes). The number of endogenous proviruses present in the random-bred flocks is highly variable, and there are proviruses present at positions in the genomes of the random-bred birds different from those described for white leghorns. The endogenous ASV-related sequences in ring-necked pheasants fall into the same two categories; sequences related to the replicative genes of ASV probably reside in proviruses, and thesrc-related sequences in a cellular gene (or genes). However, the endogenous pheasant viruses are clearly distinct from those of chickens both by analysis with restriction endonucleases and by hybridization. These observations support the hypothesis that cellularsrc (c-src) has had a separate evolutionary history from the endogenous proviruses, which apparently arise by germ line infections. The endogenous viruses of chickens and pheasants, while clearly related, appear to have undergone significant independent evolution, which suggests that the frequency with which these viruses achieve a successful germ line infection across species boundaries is low compared with the rate of successful germ line infections within a species.