Segev, O., Department of Biology, Technion-Israel Institute of Technology, 32000 Haifa, Israel
Kimchie, Z., Department of Biology, Technion-Israel Institute of Technology, 32000 Haifa, Israel
Lev, Z., Department of Biology, Technion-Israel Institute of Technology, 32000 Haifa, Israel

The expression of the Drosophila abl homologue is highly regulated during development. abl transcripts are most abundant as maternal RNA in unfertilized eggs and in early pupae. The two peaks of abl activity occur just prior to highly proliferative stages of Drosophila development: early embryogenesis and puparium formation. In a preceding step toward the understanding of the mechanisms regulating abl gene expression during development, we isolated and delimitated the abl promoter region, determined its sequence and mapped the transcription initiation sites of the abl transcripts. The results showed that the Drosophila abl gene is flanked by another transcription unit, terminating 600 to 900 nucleotides upstream to abl. The two abl transcription start sites are found within a region comprising three tandem repeats. The core sequence of these repeats may represent an inverted insect cap box. The activity of the abl promoter linked to the bacterial chloramphenicol acetyltransferase (CAT) reporter gene was demonstrated in tissue culture cells, in unfertilized eggs and in growing embryos. These experiments revealed that Drosophila eggs can also be used for the transient expression of cloned genes.