Transcriptional control of Drosophila bicoid by Serendipity delta: cooperative binding sites, promoter context, and co-evolution

Concentration of maternal BICOID (BCD) establishes the anterior pattern in the Drosophila embryo. Successive deletions in the bcd promoter allowed us to localize an enhancer sequence in the 5'-UTR and a down-regulating elemen t downstream of the ATG initiator codon, and identify a 49 bp region suffic ient to drive transcription of a reporter gene specifically in nurse cells. This fragment contains two binding sites for the Serendipity (Sry) delta z inc finger activator, that mediate its cooperative binding. Both sites (sdb s) are essential for bcd expression. Further analysis showed that the bcd p romoter configuration is decisive for Sry delta activating function. Replac ement of sdbs by binding sites for Sry beta, the Sry delta paralog, restore s bcd transcription in sry delta mutant ovaries, demonstrating that the fun ctional divergence between these two proteins during evolution was mainly d riven by changes in their DNA-specific recognition properties, resulting in the control of separate developmental pathways. (C) 1998 Elsevier Science ireland Ltd. All rights reserved.