Isolation and characterization of a retrovirus from the fish genus Xiphophorus

A cell line (BsT) established from neoplastic embryonal tissues of the platyfish (Xiphophorus maculatus) released spontaneously retrovirus-like particles. The particles have a buoyant density of 1.16 g/ml, a mean diameter of 100 nm and the morphology of immature retroviruses. The particle-associated proteins p70, p65, and p28 react with an antiserum directed against the major internal feline leukemia virus structural protein p27. The particles are associated with a reverse transcriptase. The purified enzyme has a molecular weight of about 70 kDa and prefers the template primers poly(rA):oligo(dT), poly(dC):oligo(dG), and poly(rC):oligo(dG) in the presence of Mn2+. The enzyme activity is inhibited by antibodies directed against the reverse transcriptase of feline leukemia virus and simian sarcoma virus. The particles contain a ribonucleic acid of about 70 S. In an endogenous reverse transcriptase reaction nucleic acids in the range of 0.2 to 0.4 kb were synthesized. In Northern blots with these nucleic acids as probe, three transcripts of about 8.5, 4.2, and 1.5 kb were detected in BsT cells. Southern blot analysis with the same probe demonstrates related sequences in the DNA of BsT cells and the platyfish and swordtail (Xiphophorus helleri). Hybridization experiments with the LTR-gag region of the feline leukemia virus show homologous sequences in the Xiphophorus genome.