Invertebrate retroviruses: ZAM a new candidate in D.melanogaster

ZAM , a new retroelement of Drosophila melanogaster , was identified as a mutational insertion at the white locus. It displays all the structural features of a vertebrate retrovirus. Its three open reading frames encode predicted products resembling the products of the gag , pol and env genes of retroviruses. Its transcription gives rise to an 8.6 kb full‐length RNA and a 1.7 kb spliced message for the env gene. The latter encodes an envelope protein that is typical of elements having an extracellular phase of the life cycle. The identification of a ZAM envelope retrogene provides evidence that ZAM is mobilized through a reverse trancriptional process in the germ line of flies. We report that ZAM is distributed differently among D.melanogaster strains. Two stocks out of >15 tested display a ZAM high copy number, with numerous copies distributed on chromosomal arms. This high copy number is associated with a high transcriptional rate of ZAM . The existence of these two categories of strains offers a new genetic system in which the properties of a potential invertebrate retrovirus can be tested.