Particles containing Gypsy RNA were first described in the supernatant of Drosophila cell cultures (D. melanogaster 67j25D and D. virilis 79f9 cell lines). Later, fractionation by sucrose density gradients of permissive flamenco female extracts produced low-density fractions characterized by the co-occurrence of the ENV product and an endogenous reverse transcriptase activity able to synthetize Gypsy DNA without addition of any Gypsy template. On im-munoelectron microscopic and negative staining pictures of these fractions, one can surmise particle-like structures about 100 nm in diameter, the outside of which tends to be decorated by the anti-ENV monoclonal antibodies. In the follicle cells of the same females, much smaller intracytoplasmic particles (40-45 nm in diameter, see Fig. 2), lighted up by a Gypsy DNA probe, were found to accumulate close to the membrane domains where ENV is targeted. Neither budding nor enveloped extracellular virions could be observed, as if the replication cycle of this type D-like retrovirus was somewhat abortive in this tissue.
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