A. Two distinct cases of phosphorylation‑dependent interaction modulation. Loss of interaction: the phosphorylation of one protein (A) by the active kinase results in the loss of interaction with the second protein (B) and therefore in no growth on selective media. Gain of interaction: Co-expression of an active kinase with a Y2H bait-prey protein pair can lead to phosphorylation of one protein partner (A) promoting the pS/T-dependent interaction with protein (B). In the phospho-Y2H approach, gain of interaction results in yeast growth on selective media. 