IDENTIFICATION OF SEQUENCES WHICH REGULATE THE EXPRESSION OF DROSOPHILA-MELANOGASTER DOC ELEMENTS

Long interspersed nuclear elements (LINEs) are mobile DNA elements whi ch propagate by reverse transcription of RNA intermediates. LINEs lack long terminal repeats, and their expression is controlled by promoter s located inside to the transcribed region of unit-length DNA copies. Doc elements constitute one of the seven families of LINEs found in Dr osophila melanogaster. Plasmids in which the chloramphenicol acetyltra nsferase (CAT) gene is preceded by DNA segments from different Doc fam ily members were used as templates for transient expression assays in Drosophila S2 cells. Transcription is initiated at the 5' end of Doe e lements within hexamers fitting the consensus (C/G)AYTCG and is regula ted by a DNA region which is located similar to 20 base pairs (bp) dow nstream from the RNA start site(s). The region includes a sequence (RG ACGTGY motif, or DE2) which stimulates transcription in other Drosophi la LINEs, and two adjacent elements, DEI and DE3. Moving the downstrea m region either 4 bp away from, or 5 bp closer to the RNA start site r egion inhibited transcription. Sequences located similar to 200 bp dow nstream from the Doc 5' end repressed CAT expression in an orientation - and position-dependent manner. The inhibition reflects impaired tran slation of the CAT gene possibly consequent to the interaction of spec ific Doc RNA sequences with a cellular component.