Figure 1.

Schematic representation depicting the detection of protein–protein interactions in two-hybrid systems. (A) The Y2H system: X represents a given protein fused to a specific DNA binding domain (DBD). In library screens this protein is termed the ‘Bait’. Y represents a given protein, or a pool of proteins encoded by a DNA library fused to a transcriptional activation domain (AD). This fusion protein is often termed the ‘Prey’. If X and Y interact, the AD is brought to the vicinity of the DNA bound DBD and transcription is activated from the adjacent promoter resulting in a clearly detectable phenotype. (B) The LexA repressor-based P2H system: X represents a given Bait protein fused to a mutant LexA DBD (LexA408) and Y represents a given Prey protein, or library of Prey proteins, fused to a wild-type LexA DBD (LexAWT). Interactions between X and Y produce a heterodimeric LexA repressor capable of binding to a hybrid (op⁴⁰⁸/op⁺) operator site and repressing reporter gene expression.