A 247bp enhancer fragment from Mef2 and the Hsp70Bb minimal promoter drive expression of a GAL4::GS driver composed of 65 amino acids encoding the Scer\GAL4 DNA-binding domain (providing DNA binding specificity), the hinge domain of Ecol\lexA, a truncated ligand-binding domain from the Homo sapiens progesterone receptor (resulting in the driver being activated in the presence of RU486) and the transcriptional activation domain from the Homo sapiens RELA gene. The Ecol\lexA hinge domain is used in place of more extended Scer\GAL4 sequence present in some other GAL4::GS drivers, and eliminates leaky driver activity in the absence of RU486.