CytoTrap two-hybrid system provides an alternate strategy to detect protein-protein interactions in yeast. In this system, bait protein is fused with human son of sevenless (hSos) protein (Li et al., 1993), and a cDNA library or prey protein is expressed by fusion with myristoylation signal which anchors the prey fusion protein to yeast cell membrane. Protein interaction between bait and prey proteins recruits the hSos protein to the cell membrane, where hSos activates the Ras signaling pathway, leading to the survival of temperature-sensitive Saccharomyces cerevisiae (S. cerevisiae) strain cdc25H at 36 °C. In the CytoTrap two-hybrid system, detection of protein interaction occurs in the cytoplasm near cell membrane and is not dependent on transcription activation of reporter genes. Hence, the system is particularly useful for identifying interaction partners of transcription factors and proteins that need post-translational modification in the cytoplasm, which could not be used as bait proteins in conventional transactivation-based yeast two-hybrid systems. Here we describe the construction of a cDNA library from the model plant Arabidopsis and a procedure for screening interaction proteins of AtSR1/CAMTA3, a Ca2+/CaM-regulated transcription factor from this library. This procedure could be adapted to identify interacting partners of interested proteins from other organisms.
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