The nucleotide sequences of copia and copia-related RNA in Drosophila virus-like particles

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Abstract
We have shown previously that Drosophila cells contain virus-like particles (VLPs) containing 5-kilobase (kb) RNA that hybridizes to a transposable element, termed copia. We have suggested that VLPs and copia are derivatives of viral particles and proviral forms, respectively, of ‘copia’ retrovirus, a putative Drosophila retrovirus1. To further clarify the relationship between copia and copia-related RNA in VLPs (VLP H-RNA), we determined and compared their nucleotide sequences. VLP H-RNA was found to be an unspliced, genome-sized transcript of copia, and, like retroviral genome RNA, VLP H-RNA is terminally redundant with termini localized in the long terminal repeats (LTRs) of copia. VLP H-RNA contains two long open reading frames (ORFs), one of which includes the coding sequence for a predominant VLP protein of relative molecular mass (Mr) 31,000 (31K). Here we show that, in contrast to 17.6 ORF2 (ref. 2), ORFs of copia have no extensive amino-acid sequence homology to the RT region2 of the reverse transcriptase of retrovirus in vertebrates. Because of a one-base insertion/deletion, the two ORFs in VLP H-RNA are fused and become a single, longer ORF in a genomic copia.