The reporter, SNR6, is essential for Saccharomyces cervisiae growth. The yeast indicator strain QYN1 contains an SNR6-UAS G cassette in place of the chromosomal copy of the SNR6 gene. When bait and prey interact, the AD recruits Pol III, activating expression from the chromosomal SNR6. Incubation on plates containing 5-FOA screens out cells dependent on the plasmid copy of SNR6 for growth. This system is useful for studying many protein-protein interactions, especially those thought to be involved in the regulation of the Pol II pathway.
Most traditional systems are less effective at detecting interactions between cytoplasmic proteins.
Thus, proteins that depend on post-translational processing in the ER or cytoplasm for function, proteins involved in transcriptional regulation, and those needing cytosolic or membrane entities, are ideal subjects for this system. The CytoTrap system is based on reconstitution of the Ras signaling pathway rather than on transcriptional activation. Activation of the Ras pathway, and cell growth and survival, are dependent on this protein. The target protein or cDNA library is expressed as a fusion with the Src myristylation signal, which anchors it to the cytoplasmic surface of the cell membrane. The bait protein is fused with hSos.