The UASz entry in FlyBase represents an engineered regulatory region that includes UAS 'upstream activation' sequences plus a promoter fragment derived from Hsp70, in which the Hsp70 fragment has been truncated to only contain 19bp of Hsp70 5'UTR. The remaining 5'UTR sequence is shorter than a single piRNA, and is designed to prevent Hsp70-directed piRNAs that are produced in the female germline from being able to target and silence mRNAs expressed from the UASz regulatory sequence. UASz functions better than UASp in the female germline and is comparable to UASt in many, but not all, somatic tissues (FBrf0239059). The UAS regulatory sequence present in UASz is specifically bound by the DNA-binding domain of the Saccharomyces cerevisiae GAL4 gene ( SGDID:S000006169 ) (PMID:3886158). This property can be utilized to form a binary expression system to control the spatial and temporal expression of a gene of interest: a transgene or modified endogenous locus in which the target gene of interest is downstream of the UASz regulatory region can be combined with a transgene or modified endogenous locus encoding any 'driver' that includes the GAL4 DNA-binding domain plus a transcriptional activation sequence.