The two-hybrid assay,checking for interactions between two proteins, here called Bait and Prey. (a) Gal4 transcription factor gene produces two domain proteins (BD and AD), which are essential for transcription of the reporter gene (LacZ). (b) and (c), Two fusion proteins are prepared: Gal4BD + Bait and Gal4AD + Prey. None of them is usually sufficient to initiate the transcription (of the reporter gene) alone. (d) When both fusion proteins are produced and the Bait part of the first interacts with Prey part of the second, transcription of the reporter gene occurs (adapted from http://www.wikimediafoundation.org/).
