A UAS site substitution approach to the in vivo dissection of promoters: interplay between the GATAb activator and the AEF-1 repressor at a Drosophila ecdysone response unit
V. Brodu et al., A UAS site substitution approach to the in vivo dissection of promoters: interplay between the GATAb activator and the AEF-1 repressor at a Drosophila ecdysone response unit, DEVELOPMENT, 128(13), 2001, pp. 2593-2602
An ecdysone response unit (EcRU) directs the expression of the Fat bony pro
tein 1 (Pbp1) gene in the third instar larval Drosophila fat body. The tiss
ue-specific activity of this regulatory element necessitates the binding of
both the ligand-activated EcR/USP ecdysone receptor and GATAb, To analyze
the role played by GATAb in the regulation of the Fbp1 EcRU activity, we ha
ve replaced the GATA-binding sites GBS1, GBS2 acid GBS3 in the Fbp1 EcRU wi
th UAS sites for the yeast GAL4 activator and tested the activity of the mu
tagenized Fbp1 EcRUs in transgenic lines, either in the presence or absence
of ubiquitously expressed GAL4, Our results reveal that GATAb plays two di
stinguishable roles at the Fbp1 EcRU that contribute to the tissue-specific
activity of this regulatory element. On the one hand, GATAb mediates a fat
body-specific transcriptional activation. On the other hand, it antagonize
s specifically in the fat body a ubiquitous repressor that maintains the Fb
p1 EcRU in an inactive state, refractory to activation by GAL4. We identifi
ed this repressor as AEF-1, a factor previously shown to be involved in the
regulation of the Drosophila Adh and yp1-yp2 genes. These results show tha
t, for a functional dissection of complex promoter-dependent regulatory pat
hways, the replacement of specific regulatory target sites by UAS GAL4 bind
ing sites is a powerful alternative to the widely used disruption approach.