Production of virus-like particles by the transposable genetic element, copia, of Drosophila melanogaster.

Using the calcium-phosphate procedure the plasmid cDm2055, which carries the copia transposable element of Drosophila melanogaster, was co-transfected with the Neor-carrying plasmid pSVCneo-1 into the D. hydei cell line KUN-DH-33 which was free of copia. The Neor transfectants stably carried both plasmids as tandem oligomers integrated in the chromosome and virus-like particles (VLP) were produced specifically in the transfectants that received the copia plasmid. The particles were quite similar in various aspects such as size, morphology, density, RNA content and molecular weight of the major protein component, to retrovirus-like particles (RVLP) that spontaneously appear in cultured cells of D. melanogaster: the reverse transcriptase activity however seemed to be low compared to that of the D. melanogaster RVLP. This finding demonstrates that the retrovirus-like particles (RVLP) in Drosophila cultured cells are produced by the transposable genetic element copia resident in the host chromosomes.