The Drosophila “split GAL4” system is described in Luan et al., 2006. The system involves one construct that expresses a GAL4 DNA binding domain-leucine zipper motif fusion protein and another construct that expresses a leucine zipper motif-transcriptional activation domain fusion protein. Expression of each construct may be driven by different enhancers and promoters. GAL4 activation of UAS constructs will occur only in cells where both constructs are expressed and where the two fusion proteins can dimerize via their leucine zipper motifs.