Figure 1

The split-ubiquitin system. The C-terminus of the protein of interest (bait) is fused to the C-terminal half of ubiquitin (Cub) followed by the PLV transcription factor. The N-terminal half of ubiquitin (Nub) is fused to the N- or C-terminus of a potential interactor (prey). Prey and bait fusion proteins are co-expressed in yeast with reporter genes HIS3 and LacZ under control of the LexA promoter. If prey and bait interact (left), Nub and Cub form a quasi-native ubiquitin structure which is recognized by cytosolic ubiquitin-specific proteases (red arrow). These cleave C-terminally of Cub and release PLV to activate transcription of HIS3 and LacZ. If prey and bait do not interact (right), Nub and Cub do not associate, PLV remains tethered to the bait, and HIS3 and LacZ remain silent.