Fig. 16. Activation of an indicator gene by interaction of an "interacting protein" with a "bait" protein. The bait protein is fused to a domain that binds a specific DNA sequence (binding site), and the interacting protein is fused to a domain capable of interacting with the transcription apparatus and thereby stimulating transcription. Fusion within these two hybrid proteins is indicated by the transparency effect. The indicator gene is usually one whose product can easily be assayed (e.g. LacZ, encoding beta-galactosidase) or whose product is essential for growth (e.g. HIS3 or LEU2).