jockey, a mobile Drosophila element similar to mammalian LINEs, is transcribed from the internal promoter by RNA polymerase II.

The mobile element jockey is similar in structural organization and coding potential to the LINEs of various organisms. As demonstrated here, two polyadenylated jockey transcripts detected at different stages of Drosophila ontogenesis and in cell cultures have the same length as genomic copies of jockey and correspond to the strand containing ORFs. alpha-amanitin experiments indicate that jockey is transcribed by RNA polymerase II. Analysis of both expression of CAT constructions and initiation of transcription in jockey genomic and transfected copies has shown that jockey transcription is controlled by an internal promoter. Inward location of the promoter allows it to be preserved in the course of replication via reverse transcription and accounts for the distribution of jockey and probably other LINEs throughout the genome. This is the first case of an internal promoter described for RNA polymerase II. The comparison of sequences at the beginning of LINE elements in Drosophila allows one to detect possible core sequences.