Presence of retrovirus reverse transcriptase-related gene sequences in avian cells lacking endogenous avian leukosis viruses.

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Abstract
Using a molecularly cloned viral DNA probe representing the entire avian sarcoma virus (ASV) reverse transcriptase (pol) gene, related sequences in DNA preparations were detected from 2 avian species, ev- chickens and Japanese quail, previously demonstrated to lack all endogenous avian leukosis viruses. Nucleotide sequence homology was detected only when hybridization conditions, which allowed the formation of stable duplexes with as much as 30% base mismatch, were used. No sequence homology could be detected when stringent hybridization conditions were used. Nucleotide sequence analysis of a clone representing the major pol-specific EcoRI restriction fragment from ev- chicken embryo fibroblasts revealed DNA homology as high as 72% and implied amino acid homology as high as 82% when compared to the sequence of the ASV strain Prague C pol gene. These data reveal the presence of retroviral pol gene sequences in avian cell lines that lack endogenous retrovirus sequences, suggesting that a reverse transcriptase-related gene exists in these cells as either part of a more distantly evolved retrovirus or a cellular gene.