The development and gradual improvements of the yeast two-hybrid system (Y2H) since the early 90’s revolutionized the way protein interactions could be detected1.
Yeast two-hybrid is based on the reconstitution of a functional transcription factor (TF) when two proteins or polypeptides of interest interact. This takes place in genetically modified yeast strains, in which the transcription of a reporter gene leads to a specific phenotype, usually growth on a selective medium or change in the color of the yeast colonies. The most popular reporter genes are HIS3 to select yeast on a medium lacking histidine, and LacZ to screen yeast in a colorimetric assay.
The technical details of a Yeast Two-Hybrid Assay are outlined in the cartoon below.
Two fusions (‘hybrids’) are constructed between each protein of interest and either the DNA Binding Domain (DBD) or the Activation Domain (AD) of the TF. The protein fused to the DBD is referred to as the ‘bait’, and the protein fused to the AD as the ‘prey’.
Upon interaction between the bait and the prey, the DBD and AD are brought in close proximity and a functional TF is reconstituted upstream of the reporter gene. The most popular fusions use the DBD and AD of the yeast TF Gal4. The bacterial protein LexA is also frequently used as a DBD in combination with Gal4 AD.
As a genetic technique, a yeast two-hybrid screen offers a sensitive and cost-effective mean to test the direct interaction between two targeted proteins, or to use one’s favorite protein as a bait to screen libraries of proteins fragments prepared from the desired cell types, tissues or entire organisms. The identity of the interacting partners is then obtained by sequencing the corresponding plasmids in the selected yeast colonies. Collections of full-length proteins (‘ORFeomes’) are also becoming available for several species, but they do not cover the entire proteome yet.
The yeast two-hybrid system was rapidly adopted by the scientific community and screens in various species and research fields already led to dozens of thousands of publications. It remains the method of choice when it comes to discover novel protein interactions, as reflected by the recently published literature.
Variations of Y2H were developed to conduct screens in the presence of a co-factor, or an enzyme required for a given post-translational modification of the protein partners2.
Other versions allow to screen integral membrane proteins3 and the technique was adapted to detect protein-protein interactions in mammalian cells4. Finally, yeast n-hybrid protocols were also devised to screen for novel DNA-protein5, RNA-protein6 and small molecule-protein interactions7.
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1. Fields, S. and Song, O. A novel genetic system to detect protein-protein interactions (1989) Nature 340, 245-246
2. Naba, A., Reverdy, C., Louvard, D. and Arpin, M. Spatial recruitment and activation of the Fes kinase by ezrin promotes HGF-induced cell scattering (2008) EMBO J. 27(1), 38-50
3. Stagljar, I., Korostensky, C., Johnsson, N. and te Heesen, S. A genetic system based on split-ubiquitin for the analysis of interactions between membrane proteins in vivo (1998) PNAS 95(9), 5187-5192
4. Eyckerman, S. , Verhee, A., der Heyden, J.V., Lemmens, I., Ostade, X.V., Vandekerckhove, J. and Tavernier, J. Design and application of a cytokine-receptor-based interaction trap (2001) Nat Cell Biol. 3(12), 1114-1119
5. Li, J.J. and Herskowitz, I. Isolation of ORC6, a component of the yeast origin recognition complex by a one-hybrid system (1993) Science 262(5141), 1870-1874
6. Putz, U., Skehel, P. and Kuhl, D. A tri-hybrid system for the analysis and detection of RNA--protein interactions (1996) Nucleic Acids Res 24, 4838-4840
7. Licitra, E.J. and Liu, J.O. A three-hybrid system for detecting small ligand-protein
receptor interactions (1996) PNAS 93(23), 12817-12821