The GAL4::LymRXR entry in FlyBase represents a ligand-inducible transcriptional activator that is composed of the DNA-binding domain from the Saccharomyces cerevisiae GAL4 gene ( SGDID:S000006169 ) fused to the hinge and ligand-binding domain from the Lymnaea stagnalis retinoid X receptor (RXR, UniProtKB:Q5I7G2). The GAL4 DNA-binding domain can bind specifically to the UAS regulatory sequence, but in the case of GAL4::LymRXR, the presence of the RXR ligand-binding domain means that this binding, and subsequent transcriptional activation, only occurs in the presence of the RXR ligand. GAL4::LymRXR thus acts as a 'sensor' that can potentially be used to detect endogenous retinoid activity in vivo. It can also potentially be used as a driver 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 GAL4::LymRXR. In this latter case, an exogenously supplied ligand or analog is used to ectopically activate the driver; GAL4::LymRXR has been shown to be activated by 9-cis retinoic acid (RA), all-trans RA, and two synthetic agonists (SR11237 and to a much lesser extent EC23) (FBrf0254379).