ملف:Two hybrid assay.svg

Overview of two-hybrid assay, checking for interactions between two proteins, called here Bait and Prey.
A. Gal4 transcription factor gene produces two domain protein (BD and AD) which is essential for transcription of the reporter gene (LacZ).
B,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 Bait part of the first interact with Prey part of the second, transcription of the reporter gene occurs.