Two-Hybrid Interactions Confirmed by Coimmunoprecipitation of Epitope-Tagged Clones

Abstract

The yeast two-hybrid system is a powerful genetic assay for detecting interacting proteins in yeast. The system is based on the ability of a pair of hybrid proteins, one containing a DNA-binding domain (DBD) and the other a transcriptional activation domain (AD), to interact and activate transcription of a reporter gene (1). One of its most useful applications is that of screening expression cDNA libraries to identify proteins that interact with a bait protein (2). In one widely used system, a yeast strain expressing a bait protein fused to a DBD is transformed with a library engineered to express cDNA fragments fused to an AD. The transformants are first selected based on expression of a HIS3 reporter gene and subsequently screened for expression of a lacZ reporter (2). A library screen generally yields many clones that need to be evaluated for specificity of interaction with the bait protein. Some false positives activate transcription when coexpressed in yeast with fusions unrelated to the target protein and can be eliminated by various methods (3,4).