Principle of Fluc PCA (A) Fluc is dissected into two parts, N-terminal domain and C-terminal domain. Each fragment is fused to one of interacting partners, respectively. When interacting partners are far apart, luminescence is not observed. (B) When PPI occurs, the two Fluc domains come close. (C) Upon reconstitution, the luminescence is markedly increased. (D) When the PPI inhibitor is added, the luminescence is diminished.