Double-stranded sequences in RNA of Drosophila melanogaster: relation to mobile dispersed genes

Double-stranded RNA (dsRNA) sequences were isolated from either total RNA or cytoplasmic poly(A)+RNA of D. melanogaster culture cells using a method described previously /1,2/. Virtually all dsRNA was found to be of high molecular weight (> 200 base pairs) and unable to snap back after RNA melting. Thus, it corresponds to one of dsRNA classes found in mouse cells, namely, to dsRNA-A /3/. Three different cloned DNA fragments of D melanogaster which hybridized to melted dsRNa were selected among 100 randomly taken. All of them efficiently bound poly(A)+RNA and high percentage of total cellular DNA. According to these and other properties, they were assigned to a group of mobile dispersed genes of D. melanogaster. DsRNA hybridizes to all subfragments of the two mobile dispersed genes tested (mdg 1 and mdg 3). Thus, complete transcripts of mobile dispersed genes are present in dsRNA. In total RNA, transcripts from one strand are more abundant than those from another one. DsRNA is heavily enriched in the transcripts from mobile dispersed genes as compared to total or poly(A)+RNA of the cytoplasm. It has been suggested that dsRNA in D. melanogaster is formed as the result of symmetric transcription of mobile dispersed genes. At least in the cytoplasmic fraction, two complementary strands are separated in vivo and may combine during the isolation of RNA.