The GAL4::Sp1 entry in FlyBase represents an artificial transcriptional activator ('driver') that includes the DNA-binding domain from the Saccharomyces cerevisiae GAL4 gene ( SGDID:S000006169 ) and a transcriptional activation domain from a mammalian Sp1 gene. The exact sequence of the driver may differ depending on the particular transgene or modified endogenous locus being used. The GAL4 DNA-binding domain binds specifically to the UAS regulatory sequence, and thus UAS and GAL4::Sp1 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::Sp1 driver.