Combinatorial activity of pair-rule proteins on the Drosophila gooseberry early enhancer

The early expression of the Drosophila segment polarity gene gooseberry (gs b) is under the control of the pair-rule genes. We have identified a 514-bp enhancer which reproduces the early gsb expression pattern in transgenic f lies. The transcription factor Paired (Prd) is the main activator of this e nhancer in all parasegments of the embryo. It binds to paired-and homeodoma in-binding sites, which are segregated on the enhancer. Using site-directed mutagenesis, we have identified sites critical for Prd activity. Negative regulation of this enhancer is mediated by the Even-skipped protein (Eve) i n the odd-numbered parasegments and by the combination of Fushi-tarazu (Ftz ) and Odd-skipped proteins in the even-numbered parasegments. The organisat ion of the Prd-binding sites, as well as the necessity for intact DNA bindi ng sites for both paired- and homeodomains, suggests a molecular model wher eby the two DNA-binding domains of the Prd protein cooperate in transcripti onal activation of gsb. This positive activity appears to be in competition with Eve and Ftz on Prd homeodomain-binding sites. (C) 2000 Academic Press .