A boss promoter drives expression of sequence encoding the secreted extracellular domain of boss fused to a leucine zipper derived from the Saccharomyces cerevisiae GCN4 gene (GCN4 sequence starts at residue 251, which shortens the α-Helix of the GCN4 coiled-coil domain by two amino acid residues). The presence of the leucine zipper results in the protein produced forming dimers.
Ectopic expression in wild type or boss1 mutant eye discs does not induce extra R7 cells.