The Unk(AD)::Zip+ entry in FlyBase represents a hemidriver that contains a transcriptional activation domain fused to the Zip+ heterodimerizing leucine zipper (the EE[[12]]RR[[345]]L zipper from PMID:11344333), but where the origin of the transcriptional activation domain is unknown or not specified. Unk(AD)::Zip+ forms one half of a 'split driver' system: when combined in vivo with a hemidriver containing a DNA-binding domain fused to the Zip- heterodimerizing leucine zipper (the RR[[12]]EE[[345]]L zipper from PMID:11344333), the interaction between the Zip+/Zip- heterodimerizing pair can reconstitute 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, a split driver system can be used to drive expression in a restricted pattern. The Unk(AD)::Zip+ hemidriver is compatible with any DNA-binding domain hemidriver containing the Zip- domain. The DNA-binding specificity of the reconstituted transcriptional activator will depend upon the DNA-binding domain present in the DNA-binding domain Zip- hemidriver.