The GAL4(esn) driver encodes a transcriptional activator that corresponds to a form of the Saccharomyces cerevisiae GAL4 gene ( SGDID:S000006169 ) with an internal deletion. It consists of GAL4 amino acid residues 1-147 (includes the DNA-binding domain) fused to GAL4 amino acids 768-881 (includes transcriptional activation sequence) (PMID:20418862). The GAL4 DNA-binding domain binds specifically to the UAS regulatory sequence, and thus GAL4(esn) and UAS form a binary expression system that can be used to control the spatial and temporal expression of a gene of interest: a transgene or modified endogenous locus carrying the target gene of interest downstream of UAS sequences is combined with a second transgene or modified endogenous locus encoding the GAL4(esn) driver.