AN ENHANCER-REGION WITHIN THE COPIA UNTRANSLATED LEADER CONTAINS BINDING-SITES FOR DROSOPHILA REGULATORY PROTEINS

The untranslated leader region (ULR) of the Drosophila LTR retrotransp oson copia is known to be critical to the element's expression in a va riety of species. Two copia ULR size variants are prevalent in natural populations. The more transcriptionally active full length variants c ontain within their ULRs two tandemly repeated copies of a 28-bp regio n of dyad symmetry with a sequence similarity to the core sequence of the SV40 enhancer. The region of dyad symmetry contains two inverted r epeats of a 8-bp motif (TTGTGAAA) that occurs at three additional loca tions within the ULR. The less active ULR gap variants differ from ful l length variants in that they contain only one copy of the 28-bp sequ ence. We show that the full length copia ULR in either orientation but not the gap ULR can significantly enhance expression of a minimal hsp 70 promoter. We demonstrate by EMSA that the full length ULR, the gap ULR and the 28-bp sequence are each capable of binding the Drosophila CCAAT/enhancer binding protein (DmC/EBP) and another previously uncha racterized factor, copia binding factor-1 (CRF-I). Another Drosophila protein previously implicated in fat body specific expression of the a lcohol dehydrogenase gene (Adh), the Box-B-binding factor-2(BBF-2), is also shown to bind to the copia ULR. (C) 1998 Elsevier Science B.V.