Abstract
A detailed investigation of Drosophila melanogaster mobile dispersed repetitive element jockey is performed. Its structural features resemble those of LINE elements. Sequencing of the complete jockey 5020 bp in length revealed two long open reading frames ORF1 and ORF2 overlapping with a frameshift-1. Judging by amino acid homologies, ORF1 encodes a nucleic acid binding protein, characteristic of replication competent retroviruses; the 3' part of ORF2 encodes an RNA-dependent DNA polymerase which has an amino acid sequence, similar to recently published sequences of LINE elements of Drosophila, Trypanosoma and mammals. This fact demonstrates their evolutionary relationship. Sequencing of several deleted copies of jockey revealed the absence of the major part of ORF2, though the rest of the element, including the ends, is highly conservative. A detailed investigation of the Drosophila melanogaster mobile dispersed repetitive element jockey was performed. This is similar in its structural organization and coding potential to the long interspersed elements (LINEs) of various organisms. A complete copy of jockey (approx. 5 kb) is terminated with an oligodeoxynucleotide (dA) sequence preceded by two long open reading frames (ORFs) overlapping with a frameshift-1. Judging by the sequence homologies, ORF1 codes for a nucleic-acid-binding protein, and ORF2 for a reverse transcriptase which is most similar in its sequence to putative reverse transcriptase of other LINEs. As demonstrated by sequencing two deleted jockey copies, they contain only a small part of ORF2; however, other regions, including the terminal sequences, are highly conservative. The existence of a large number of jockey copies with a deletion in the second frame may indicate that they can use reverse transcriptase in trans.
