The detection of intracellular retrovirus-like entities in Drosophila melanogaster cell cultures.

A Drosophila melanogaster cell line has been examined for the presence of retrovirus particles. When these cells were disrupted and analysed on sucrose density gradients a subcellular fraction with a density of 1.22 g/ml was found to possess endogenous DNA polymerase activity and could catalyse polymerization of deoxynucleotide triphosphates in response to added template primers. The latter activity had the cation and template primer responses expected for reverse transcriptase. A high mol. wt. polyadenylic acid-containing RNA was also purified from this fraction and could be dissociated by heat treatment into 30 to 35S and smaller species. Electron microscopy revealed the presence of torroidal forms reminiscent of intracytoplasmic A-type retrovirus particles within the Drosophila cells. Similar forms were found associated with the subcellular fraction of 1.22g/ml. We concluded that our D. melanogaster cell line contains retroviruses similar, but not identical, to the A-type particles previously described in mammalian and avian cells.