GAL4(GTD-a) and GAL4(GTD-b) form the two halves of a Split GAL4 system. The GAL4(GTD-b) hemidriver consists of the DNA-binding domain from the Saccharomyces cerevisiae GAL4 gene ( SGDID:S000006169 ) fused in frame to the coding sequence of the Mus musculus Trp53 gene (MGI:MGI:98834). The GAL4(GTD-a) hemidriver consists of the GAL4 activation domain fused to the SV40 large T antigen, a binding target of Trp53. When the two hemidrivers are combined in vivo, Trp53 can bind to the SV40 large T antigen, bringing the GAL4 DNA-binding and activation domains together and reconstituting a functional transcriptional activator that can drive transcription of a downstream gene of interest. Since transcription is only activated at the intersection of the expression patterns of the two hemidrivers, the Split GAL4 system can be used to drive expression in a restricted pattern. The reconstituted transcriptional activator binds specifically to the UAS regulatory sequence due to the presence of the GAL4 DNA-binding domain (FBrf0132344).