Yeast transformed with different cDNA clones were plated onto agar media lacking essential nutrients: uracil, leucine, and/or histidine. For each pair, the regulatory domain of SPAK was fused to the GAL4 activating domain in pACT2, and a 12 amino acid peptide (sequence on the right inset) was fused to the GAL4 binding domain in pGBDUc2. (A): control plate lacking two essential nutrients (uracil and leucine) to demonstrate transformation efficiency. (B) Yeast survival on plate lacking three essential nutrients (uracil, leucine, and histidine) exists only upon interaction between the GAL4 fusion proteins translated from each clone.