[Organization of promotor regions in Drosophila retrotransposons]

The absence of TATA-box-like sequences and the presence of TCAGT sequences in the region of transcription initiation is the common feature of a number of Drosophila retrotransposons (e.g. mdg1, mdg3, mdg4). To reveal the LTR sequences, responsible for the transcription, a series of deletion mutants, containing a bacterial gene of chloramphenicholacetyltranspherase (CAT) under the control of different LTR fragments of these mdgs, was constructed. Such constructions were transfected into Drosophila Schneider2 cultured cells and the CAT-activity was analysed. The transcription of these constructions was also investigated by Northern blot hybridization and primer extention methods. The analysis of mdg1 promoter region showed, that it has two different elements. The distal one is responsible for the RNA synthesis level, while the proximal one is localized in the site of transcription origin and is responsible for the precision of transcription initiation. Therefore, a new type of RNA-polymerase II promoter elements, responsible for the accuracy of transcription initiation was revealed. The analysis of mdg3 and mdg4 promoters showed, that these retrotransposons also have such elements, but in contrast to mdg1, they have no promoter sequences analogous to the distal one in mdg1.